| By Author | [ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | Other Symbols ] |
| By Title | [ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | Other Symbols ] |
| By Language |
|
Download this book: [ ASCII | HTML | PDF ] Look for this book on Amazon Tweet |
Title: Garden Pests in New Zealand - A Popular Manual for Prictical Gardeners, Farmers and Schools
Author: Miller, D.
Language: English
As this book started as an ASCII text book there are no pictures available.
*** Start of this LibraryBlog Digital Book "Garden Pests in New Zealand - A Popular Manual for Prictical Gardeners, Farmers and Schools" ***
Transcriber’s notes:
In this transcription, paired _underscores_ denote italicised text.
Archaic spellings such as ‘sedementary’ and ‘millepedes’ have not
been altered, and the following spelling inconsistencies have also
been left as in the original text: omnivorous/omnivorus,
eleagnus/elæagnus, silverfish/silver-fish, woodlice/wood-lice,
blowfly/blow-fly.
The following typographic errors have been corrected:
kindom —> kingdom
aphis lion —> aphis-lion
Jose —> José
ocurring —> occurring
necesary —> necessary
Crytolæmus —> Cryptolæmus
Crape —> Grape
pupuli —> populi
CAWTHRON INSTITUTE MONOGRAPHS
GARDEN PESTS
_in_
NEW ZEALAND
_A Popular Manual
for
Practical Gardeners, Farmers
and Schools_
By
DR. D. MILLER
Ph.D., M.Sc., F.R.S.N.Z., F.R.E.S.
Assistant Director and Chief Entomologist,
Cawthron Institute, Nelson
CONTENTS.
Page
Introduction 5
Chapter i.: General Review of the Animal Kingdom 7
Chapter ii.: Soil Organisms and Soil Fertility 12
Chapter iii.: Structure of Insects 17
Chapter iv.: Life Histories of Insects 22
Chapter v.: Sucking Insects 29
Chapter vi.: Sucking Insects (Concluded) 42
Chapter vii.: Leaf-feeding Insects 50
Chapter viii.: Boring and Underground Insects 61
Chapter ix.: Miscellaneous Pests 67
Chapter x.: Principles of Pest Control 74
Index 81
_Introduction_
This work deals with the insects and other animals having a detrimental
or beneficial influence upon horticulture in New Zealand. Its purpose
is to supply such general information as will enable the common animal
inhabitants of the garden to be identified and controlled, to act as a
popular guide for the use of practical gardeners and schools, and at
the same time serve as a source from which the examination requirements
set out in the syllabus of the New Zealand Institute of Horticulture
may be met.
As this work is for the benefit of the gardening public, and an
endeavour to diffuse some knowledge of certain natural problems, the
language of the scientist--which, unfortunately, tends to guard what
is known of these problems from the general reader--has been avoided
as much as possible; at times, however, this ideal cannot be adhered
to, but in such cases the reader should find no difficulty, and should
be prepared to become familiar, with the few terms used. To know the
scientific names of animals without being acquainted with the animals
themselves is a habit to be avoided, and is just about as instructive
as memorising the names of people in a town or telephone directory.
But animals must be named; though their popular names are used in
the following pages and as such names are very often misleading, the
scientific names are given in brackets in order to avoid confusion.
In such a work as this, illustrations are of great value, and these
are given wherever possible. One drawback to illustrations is that the
relative proportions of animals may be lost; for example, a microscopic
organism might require magnification by some 4,000 times its natural
size and so become equal to that of some of the most conspicuous
insects. Even with the best illustrations, however, it is essential
that the reader becomes familiar with the animals themselves. This
should present no difficulty to the reader, since he will find in his
garden all of the animals with which he is concerned--mostly insects
and their near relatives. Further, of very great assistance to him, he
will find the several excellent public museums throughout the country,
as well as the specialists at such research institutions as the
Cawthron Institute at Nelson.
To keep a work for the general reader in a readable form, the desire of
the author to cite the sources from which he derives his information
must be suppressed. If this were not done, the text would rapidly
become littered with endless references, much to the weariness and
confusion of the reader. Therefore, it should be remembered that a work
of this kind is a compilation from the publications of many scientists,
to which is added what little original information the writer himself
might possess.
Opportunity must be taken here to express one’s appreciation of the
assistance given by Mr. W. C. Davies and Mr. L. J. Dumbleton in the
preparation of the photographs and drawings, respectively.
CHAPTER I.
General Review of the Animal Kingdom.
At the outset it is advisable, by reviewing the animal kingdom as a
whole, to secure in perspective the relationships of the animals with
which the horticulturist has to deal.
To most people the animal kingdom is comprised chiefly of those animals
commonly met with in everyday life or in general reading--the game and
domestic animals and the fishes, all of which are similar in that they
possess a backbone or vertebral column, and are consequently known as
the vertebrates. Popularly, however, they are generally classed as the
“lower” and “higher” animals; there is certainly some accuracy in such
a haphazard classification, since, though all the vertebrates are,
strictly speaking, the “higher” animals, some are “lower” (_e.g._,
fish, frog, and bird) than others (_e.g._, kangaroo, dog, and man, the
highest of all).
But when it comes to the true “lower” animals, that vast assemblage
of less conspicuous creatures, the jelly-fish and corals, worms of
all kinds, sea-urchins, crayfish, wood-lice, spiders and insects,
shell-fish and snails, all characterised by the absence of a vertebral
column and known as the invertebrates, they are not collectively
visualised in a general sense as are the vertebrates. As a rule, these
invertebrates are known individually as independent units, except,
perhaps, in the case of worms, insects, spiders, wood-lice, etc., which
are very often collectively and haphazardly referred to as “insects,” a
term, in this sense, as ill-defined as it is unlimited.
That the average person should be more conversant with the vertebrates
than the invertebrates is, to a great extent, the natural outcome
of association and training; a possible influence is to be found at
the outset of one’s career in the many illustrated nursery books
depicting game and domestic animals, but seldom, if ever, any of
the invertebrates; and this impression tends to be further fostered
in later life by visits to the zoo, where we meet in person most of
the nursery book animals, and perhaps some of the lower forms, such
as insects; but the latter, in most cases, are there by chance, not
design, and against the will of the authorities.
In recent years, however, more public attention has been given to
the lower animals owing to the detrimental influence of many upon
agricultural development as well as upon public health. That such
animals are capable of ranking as fundamental factors hindering
human progress, may be realised when it is considered that, of the
invertebrates, insects alone comprise nearly four-fifths of the whole
animal kingdom! This has been graphically illustrated as follows by
F. E. Lutz, of the American Museum of Natural History:--Extend the arms
and fingers at right angles to the body, and let the distance from the
tip of the middle finger of one hand to that of the other represent
the number of different kinds of living animals; then the last joint
of the middle finger of the right hand will be proportionate to the
number of mammals (kangaroos, hoofed animals, rabbits, man, etc.), the
second joint to the reptiles and their relations, the first joint to
the birds, and the distance between the knuckles and the wrist to the
fishes. “In other words, you can hold the so-called zoological gardens
and their aquarium annexes in one hand.” Finally, the distance between
the wrist of the right arm and the tip of the middle finger of the left
will proportionately represent all the known species of invertebrates,
and of this section of the extended arms all except between a wrist and
an elbow will be insects.
The zoologist classifies the animals under twelve main divisions,
of which eleven contain the invertebrates and one the vertebrates;
these divisions are arranged in a series, the first containing the
simplest or lower animals, and the last the most complex or highest.
A glance at this classification will serve to give some idea of the
relative position in the animal kingdom of the animals which will be
dealt with in the following pages. The very lowest forms, belonging to
the first division, are micro-organisms known as the Protozoa; they
inhabit water and soil, and live upon their own kind or upon minute
plants, including bacteria, or are parasitic upon the higher animals,
some of these parasites causing such diseases as malaria. The Protozoa
are single units of living matter (protoplasm), and may be referred
to as the one-celled animals; they are mostly microscopic, and lead
an independent life, or are associated in colonies, but are capable,
as a rule, of carrying on independently all the functions of life,
though there are no organs such as those of digestion, respiration, and
circulation, as we know them in the higher animals. It is amongst such
simple forms that the distinction between the lowest animals and plants
ceases to be clear. As will be discussed later, there is evidence that
certain Protozoa have an important influence on soil fertility.
The remaining eleven divisions contain all other animals, ranging in
size from mere specks to the mass of the elephant; the bodies of these
are built up of a complex aggregate of countless cells of protoplasm
arranged in groups to form the organs of digestion, circulation,
respiration, reproduction, etc., each having its definite function
in the animals’ lives. The following are some typical or well-known
examples of each of these divisions, the technical names, with the
exception of the Protozoa, not being given:--
The Protozoa (reference should be made here to Fig. 1) are followed
by (2) sponges; (3) jelly-fish, sea-anemones, corals; (4) flat worms
(tape-worms, etc.); (5) round worms (thread-worms, eel-worms);
(6) sea-mats, lamp-shells; (7) wheel-animalcules; (8) star-fish,
sea-urchins; (9) segmented worms (earthworms); (10) crayfish, woodlice,
centipedes, millepedes, spiders, mites, insects; (11) shell-fish,
slugs, snails; (12) fish, frogs, lizards, birds, hedgehogs, rabbits,
man.
So far we have reviewed the animal kingdom from one aspect only--that
of classification, based on the resemblances and differences of the
individuals. It is now necessary to look at the subject from the
viewpoint of the horticulturist--that is, the relationships of the
animals to their surroundings, or environment, and to the welfare of
man. Of the two great life-groups--animals and plants--the plants are
of fundamental importance; without them no animal could exist, since,
of all living things, it is the green plants alone that are able to
convert the inorganic chemical constituents in soil, air and water
into living matter or protoplasm; and all animals, either directly or
indirectly, are dependent upon plants for their food supply. Plants,
therefore, may be looked upon as the primary producers of life, and
animals as the consumers. It is in this respect that the horticulturist
becomes interested, in that certain of these consumers destroy too many
of the plants grown by him for other purposes; fortunately, not all
of the consumers are destructive; many are of very great use to the
horticulturist and mankind in general.
The last point is well illustrated by the following classification
of the animal kingdom based upon the part it plays in human welfare;
this is a modification of the scheme adopted by the British Museum of
Natural History:--
_Group I._--Wild or domesticated animals used by man as beasts
of burden, source of food, or in the manufacture of various
products--_e.g._, sponges, crayfish, bees, silk-worms, shell-fish, and
various vertebrates, as fish, birds and mammals.
_Group II._--Animals detrimental to man’s welfare, attacking man
himself; animals and plants of value to him, or the products derived
therefrom--_e.g._, Protozoa, parasitic worms, mites, insects, and such
vertebrates as certain birds and mammals.
_Group III._--Animals aiding man’s welfare, as scavengers, or by
pollinating flowers, or by attacking and checking such animals as are
included in Group II.--_e.g._, Protozoa, parasitic worms, earthworms,
parasitic insects, spiders, and such vertebrates as certain birds and
mammals.
An analysis of the above classification shows that animals both aid and
hinder the progress of man, hence the use of the terms “beneficial”
and “destructive.” In nature, however, these terms are not altogether
applicable in the same sense, since the balance maintained between
animals and plants under natural conditions is an extremely fluctuating
one, though sufficient for natural purposes; with man, however, the
case is different. In order to compete in the world’s markets, and to
supply the growing demands of increasing population, a much higher
and dependable standard of productivity is required than is found in
nature. Consequently, whilst utilising, and increasing the efficiency
of the so-called natural enemies as auxiliaries in his fight against
destructive animals, man has found it necessary to develop an effective
system of artificial control, involving chemicals, resistant plants,
cultivation, crop rotation, etc., for the purpose of maintaining a more
stringent balance to meet his requirements.
Historical Review of New Zealand Conditions.
The animal population of European New Zealand is very different from
that of pre-European times, a position brought about naturally enough
by the changes resulting from agricultural development as practised in
the Old World, and the consequent creation of an environment foreign to
the country.
Though the official date of the settlement of New Zealand by Europeans
is 1840, the influences, inaugurating that upheaval of the natural
conditions which was later to have such a marked effect on the
economic development of the country, had commenced many years earlier.
[Illustration: Fig. 1.--Some common animals grouped to represent the
twelve main divisions of the animal kingdom.]
When the first Europeans set foot in New Zealand, they must have been
impressed by their unique surroundings, totally different from anything
to be met with in the Old World. They found the country dominated by a
forest quite unlike the forests of any other land, and inhabited by an
animal population presenting many unusual features. This terrestrial
population was characterised by an abundance of insects and spiders,
and a paucity of vertebrates excepting the birds; the vertebrates
consisted of a species or two of frogs, a few species of lizards, some
200 species of birds, and two species of bats, the last being the only
terrestrial mammals. In fact, the insects, spiders and birds were the
dominant animals, a feature common to other parts of the world, but the
scanty vertebrate population, other than birds, was a characteristic of
primeval New Zealand.
New Zealand being a country fitted for agriculture, settlement by
Europeans naturally resulted in extensive and rapid changes, since
the settlers brought with them the knowledge, implements, animals and
plants of the civilised world; and to make way for settlement, it was
necessary to remove the forests and drain the swamps, and to replace
them with cultivated crops and pastures. These activities have been so
thorough, that, within a period of some 90 years practically the whole
of the original North Island forests, and the greater part of those of
the South Island, have been cleared.
An outstanding feature of these changes is that many of the pests
associated with the agricultural animals and plants have been brought
to New Zealand with the animals and plants they infest, and these
exotic pests comprise by far the greater proportion of the destructive
animal population, there being but few native species forming the
balance. For example, 71 per cent. of the destructive insects are
exotic, and 29 per cent. native, while all the parasitic worms of
economic importance, all the destructive birds (_e.g._, sparrows) and
mammals (_e.g._, deer, wild pigs, and goats) are introduced.
The exotic factors that have set up this new environment may be
summarised as follows:--
(1) Clearing of the native vegetation.
(2) Introduced plants: _e.g._, grasses, forage crops, trees, etc.
(3) Introduced game animals: _e.g._, deer, pigs, rabbits, birds,
etc.
(4) Introduced destructive animals, infesting animals and plants of
economic value: _e.g._, parasitic worms, insects, etc.
(5) Animals imported to control pests, but which have become
destructive themselves: _e.g._, weasels, birds.
CHAPTER II.
Soil Organisms and Soil Fertility.
In the first chapter the plants were referred to as the primary
producers of life, and the animals as the consumers; the former not
only furnish nourishment for their own growth, but also for the support
of the animal world as a whole. Living plants (in reference to green
plants) utilise the sun’s energy in the manufacture of their complex
food materials from comparatively simple chemical compounds. These
latter compounds are carbon dioxide, derived from the air through the
agency of leaves, and a weak solution of various chemical compounds
in water, derived by means of the roots from the soil, and carried up
through the plant to the leaves, where the elaboration into the complex
compounds to be utilised by the plants as food takes place.
These comparatively simple compounds from which the plants elaborate
their nourishment are the raw food materials, and that they must always
be available for plant growth, is evident when one considers the vast
areas of vegetation that cover, with the exception of desert regions,
the surface of the earth. Under moist climatic conditions it has been
calculated that some 500 tons of carbon dioxide and 1,000,000 tons of
water, having the raw food materials in solution, are used annually
by one square mile of dense forest. For their development, therefore,
plants require:--
(1) Sunlight as the source of energy for the carrying on of their
life functions;
(2) Air for the supply of carbon dioxide, oxygen, and, indirectly,
nitrogen;
(3) An ample supply of water required for the living tissues and as
a vehicle for the transport from the soil of
(4) The raw food materials, in the form of various chemical
compounds.
With the exception of the carbon dioxide derived from the air, all the
raw food materials--water, nitrates, phosphates, sulphates, potassium,
calcium, magnesium, iron, etc.--are present in the soil, though only
a part of them is in a form suitable for imbibition by plants. In the
formation of these food materials, which render the soil fertile,
physical forces and the activities of living organisms play a leading
part. Our immediate concern is with the influence of these organisms
upon soil fertility, but it is advisable to give some consideration to
the soil itself, since it is the environment in which the organisms
live, and with which their existence is intimately associated; in
this respect attention will be confined to the type of soil usually
cultivated by the horticulturist, and to the uppermost layers--that is,
approximately, within one foot of the surface.
Soil is the product of disintegrated and weathered rocks with which
are mixed the residues of organic matter. Apart from the particles of
disintegrated rocks, which form the matrix, soil contains chemical
compounds of two kinds: those of a purely mineral nature derived from
the inorganic components of the original rocks, and those of an organic
origin derived either from the ancient remains of organisms, which, in
the case of sedementary deposits, became incorporated in the rocks at
the time of their origin, or from the remains of present-day plants and
animals decomposed by soil organisms. In addition, there is the humus,
which has a fundamental physical influence, and for the production of
which soil organisms are responsible.
[Illustration:
Figure 2
THE THREE MAIN TYPES OF SOIL PROTOZOA.
Magnified 300-400.]
In the initial stages of soil formation during the disintegration
and decomposition of rocks, the first type of soil to be formed is
suitable for the growth of only certain plants; it is of a purely
mineral nature, containing raw food materials derived mainly from the
rocks and not from organic matter, unless from such organic residues
as were incorporated in the rocks during their formation in ancient
times. Such soil cannot sustain the higher types of green plants, nor
is it populated by soil organisms; it furnishes suitable pabulum,
however, for the nourishment and growth of the more lowly types of
vegetation, which are able to convert to their benefit the limited
supply of food materials available. The complex organic compounds that
such primitive plants elaborate from these food materials of purely
mineral origin, and incorporate in their tissues, are, after death,
returned to the soil, which becomes correspondingly enriched, and a
favourable environment for the establishment of organisms; the latter
reduce these plant residues to humus, and during this process of
decomposition produce food materials of an organic origin suitable for
the nutrition of the sequential plant covering. So the process proceeds
until a soil is formed of sufficient extent and quality for the support
of a more extensive and increasingly complex vegetation; thus, in the
cycle of life and decay, stores of organic compounds are elaborated by
plants and returned to the soil, which they enrich, and where they are
decomposed by organisms, and so maintain the supplies of food materials
suitable for the maintenance of vegetation.
These phenomena of plant establishment and succession, correlated with
soil formation, were clearly demonstrated by the re-establishment of
vegetation after the soil and plant life had been destroyed by the
historic eruption in 1883 of Krakatoa, a volcanic island in the Straits
of Sunda, between Java and Sumatra. The first plants to be established
on the volcanic deposits were species of terrestrial algæ, which
gradually spread and built up soil suitable for the development of soil
organisms and for the growth of seeds brought to the island by birds
and ocean currents. So rapid were the changes brought about by these
influences, that within a period of twenty years after the eruption the
barren ground was reclothed by a dense and varied plant covering.
Organisms that form part of the organic complex of the soil range
from the more conspicuous species, such as slugs and snails, insects,
spiders, wood lice, millepedes, earthworms and eelworms, to such
microscopic forms as protozoa, fungi, algæ and bacteria, the last three
being members of the plant kingdom. These organisms may be grouped as
follows:--
(1) Temporary inhabitants that enter the soil for shelter, or to
feed as scavengers on decaying organic matter, or both--_e.g._,
slugs, snails, wood lice, certain insects and some eelworms.
(2) Permanent inhabitants that are dependent on the soil for their
development and supplies of food, either throughout or during most
of their lives--_e.g._, certain insects and spiders, millepedes,
earthworms, eelworms, protozoa, fungi, algæ and bacteria.
The organisms in the first group play a comparatively minor part in
soil development, and influence its fertility to an almost negligible
extent, the temporary scavengers, perhaps, being of more importance
since they aid in the reduction of vegetable residues. The forms in
the second group, however, are invaluable as soil-making agents and in
the production of plant food materials, the least important among them
being the insects, spiders and millepedes. Many are merely scavengers,
but some insects, such as grass-grubs and the caterpillars of certain
moths, and millepedes, feed upon living plants and so add organic
matter to the soil in their excreta, which also contains quantities of
soil swallowed with the food, this latter mechanical action aiding in
the pulverising and opening up of the soil; certain eelworms, too, that
attack living plants play a somewhat similar part, in that they are
primary causative agents in the decay of healthy tissues. Other forms
of insects, together with spiders and some eelworms, are predaceous
upon their fellows, the remains of the latter being added to the soil
residual complex. Apart from the activities of all these organisms,
however, it is the earthworms, protozoa, fungi, algæ and bacteria that
have the most fundamental influence upon soil fertility.
Earthworms may be correctly called the great soil builders; they
burrow through it, allowing the free passage of air and water; they
swallow large quantities, which they eject on the surface in the form
of “worm-casts,” the soil materials being well mixed in the process;
they pull underground leaves and other parts of plants from the surface
and so increase the supply of organic matter for the action of the
micro-organisms that bring about decomposition. Further, by depositing
their “casts” on the surface, earthworms soon cover the accumulations
of dead vegetable matter, as has been illustrated by Darwin in his
classic work on these animals. Without the aid of earthworms--_e.g._,
in sour soils in which they do not abound--the plant residues
accumulate on the surface, to form a partially decomposed, peaty mass,
which only a limited number of plants can tolerate.
The protozoa, fungi, algæ and bacteria are all microscopic organisms,
and are the agents responsible for the decomposition of the organic
residues in the soil; they do not act as independent units, the
processes of one group being dependent upon and intimately related
with those of the others. During the activities of these organisms
various organic and mineral substances are decomposed or transformed
into materials, such as humus and the inorganic compounds of nitrogen,
phosphorus, potassium, etc., necessary or helpful for the growth of
plants.
The protozoa (see Chapter I.) are the lowest and simplest forms of
animal life, being mere specks of living matter. Three different groups
of soil protozoa occur (Fig. 2). Some, like the amœba, progress by
streaming movements, extruding temporary extensions of their substance
in the form of finger or thread-like processes; the bodies of such
protozoa may be naked, or enclosed in a shell-like covering secreted by
the organism itself, or protected by an accumulation of particles of
foreign matter. Some have a body of more definite shape and progress
by means of the whip-like action of one or two thread-like processes,
or flagella, arising from one end of the body. Such forms are the most
numerous in the soil. Others, also of definite shape, control their
movements by means of short, hair-like processes, or cilia, either
distributed over the body or restricted to definite regions.
The protozoa are widely distributed, being most abundant in the richer
types of soil, especially during the spring and autumn. A great amount
of research has been undertaken at Rothamsted, England, and elsewhere,
on the part played by protozoa in soil fertility; the evidence thus
secured points to the probability that some of these organisms may be
detrimental in that they devour certain kinds of bacteria responsible
for the production of nitrates and other substances of nutritive value
to plants. The extent of this may be realised from the fact that in a
definite weight of soil (about 1-28th of an ounce) the micro-population
was calculated to include not only about 1,550,000 protozoa, of which
430,000 were amœbæ (Fig. 2), but also some 6,000,000,000 bacteria.
Observations showed that a single bacteria-destroying amœba required
about 400 organisms for its nourishment, so that the amœbæ, to
say nothing of the other protozoa, present in the weight of soil
above-mentioned, would be capable of destroying about 172,000,000 of
the bacterial population. Since the partial sterilisation of soil by
steam results in an increase of fertility, it is thought, on account of
the sterilisation destroying the protozoa, being more susceptible, and
not the bacteria, that protozoa inhibit the activities of the bacteria
to such an extent as to reduce the fertility of the soil; but this is
a subject as yet open to argument. Apart from the bacteria-destroying
protozoa, there are other forms that are thought to have something to
do with the decomposition of organic substances.
The fungi, algæ and bacteria are amongst the lowest forms of plant
life, and hold somewhat the same position in the plant kingdom as
the protozoa do among animals; they are, especially the fungi and
bacteria, of primary importance in the maintenance of soil fertility.
The role of algæ lies mainly in increasing the organic content of the
soil, and they are invaluable in developing favourable conditions for
the establishment of vegetation on purely mineral soils. The fungi
and bacteria are responsible for setting up the intricate reactions
involved in the decomposition of organic matter, the bacteria being
concerned in practically all of the chemical processes going on in the
soil. Both fungi and bacteria are of two kinds: those that bring about
decomposition, and those that live in a reciprocal relationship with
plants upon the roots of the latter. Such relationship, which benefits
both organisms and plants, is called symbiosis, the fungi being known
as mycorrhiza, while the bacteria form nodules on the roots of such
plants as the legumes.
CHAPTER III.
Structure of Insects.
Although insects present a great variety of forms, they nevertheless
agree in general features; thus by studying the structure of some
generalised species, which will give a broad idea of the main
characteristics, one is enabled to recognise different structural
modifications assumed by various species. For this purpose a weta,
grasshopper, or cockroach may be taken as a type.
Just as in the case of the crayfish, so the body of an insect is
completely covered and protected by a continuous “shell,” very solid
in some insects, more or less pliable in others, but even in the most
delicate forms tending to become rigid and brittle after death. This
shell acts as a skeleton and as a very effective armour-plating,
protecting and supporting the soft body within. Unlike the shell of
the crayfish, which is mainly calcareous, that of insects consists of
a horny substance called _chitin_, secreted by the underlying skin,
and constitutes what is known as a _cuticle_. It is due to this horny
cuticle or shell that the form and colour of most insects are preserved
after death, though the enclosed body tissues decay unless preserved in
some suitable medium.
The cuticle, though forming a complete covering, does not enclose the
body in an inflexible shell; flexibility is allowed by the cuticle
being formed of a segmented series of strongly-chitinised sections
alternating with skin-like, feebly-chitinised, and very elastic
sections; this arrangement gives freedom of movement to the enclosed
body, as is readily seen in the movements of a caterpillar.
There are three distinctly separated divisions of the insect
body--head, thorax, and abdomen--each consisting of a varying number
of segments (Fig. 3). The head segments are so closely fused as to
be practically untraceable, the cuticle forming a rigid capsule; the
thorax, to which the head is attached, carries the wings (when present)
and the legs, and consists of three segments; posterior to the thorax
is the abdomen, comprised of several segments, which show the typical
segmentation of insects better than any other part of the body.
The head capsule is more or less freely movable on the thorax, and
bears certain sensory organs, together with the mouth appendages.
The sensory organs are the eyes and the feelers, or antennæ. On each
side is a compound eye of varying size, according to the insect; each
eye consists of a variable number (from a comparative few to several
thousand) of microscopic, hexagonal lenses, each of which records a
separate image. Between the compound eyes, on top of the head, are
three simple eyes in some insects, but in others one or all of these
may be absent. Between the compound eyes on the front aspect of the
head is a pair of feelers, or antennæ; they consist of a variable
number of joints, are freely movable and highly sensory, thread-like
or hair-like, short, or longer even than the whole body, and may be
bare or clothed to a varying degree with hair or bristles. On the
antennæ are the organs of touch, smell, and sometimes hearing.
[Illustration: FIG. 3.]
When the head of a weta, grasshopper, or cockroach is removed from
the body and boiled for a few minutes in a 10 per cent. solution of
caustic potash, and then washed in water in order to remove the muscles
and other tissues, a large opening will be seen on the posterior
surface where the head was attached to the thorax; also, if the mouth
appendages are pulled apart, they will be seen to surround another
opening on the lower aspect of the head capsule, marking the position
of the mouth. The digestive canal passes from the mouth through the
posterior opening into the thorax.
The mouth appendages are as follows (Fig. 3):--Suspended from the fore
aspect of the mouth opening is a more or less conspicuous movable
flap, which forms the upper lip, while from the posterior aspect of
the same opening is another suspended appendage forming the lower lip;
this latter appendage is really a complicated one, and bears a pair
of short, jointed appendages--the palps--which are sensory organs,
while on its inner surface--_i.e._, within the mouth--is a swollen
area or tongue, an organ very greatly modified in certain insects.
Between the upper and lower lips, and suspended from both sides of the
mouth opening, is a pair of true jaws immediately behind the upper
lip, followed by a pair of accessory jaws immediately before the lower
lip; these jaws do not move up and down, but have a side-wise action,
closing and opening like scissor blades. While the true jaws are each
of one piece, the accessory jaws consist of several parts, and each
bears in addition a jointed palp, as in the case of the lower lip. The
upper and lower lips serve to hold the food in the mouth, the true
jaws nibble or tear off portions of the food and masticate it (if the
term can be used), while the accessory jaws, aided by the lower lip,
manipulate the food during the process of feeding.
The comparatively simple arrangement of mouth parts found in the weta,
grasshopper, and cockroach, as described above, is characteristic of
all insects that gnaw or chew their food--_e.g._, earwigs, beetles
and their larvæ or grubs, the caterpillars of moths, and so on. There
is, however, a vast number of insects that has developed more or less
complex variations of this generalised pattern, according to the manner
of feeding.
The mouth parts of the worker honey-bee, for example, have the jaws
adapted for eating pollen and moulding wax for the comb; the accessory
jaws, however, are lengthened, though their palps are reduced to
mere vestiges in contrast with the elongated palps of the lower lip;
the most remarkable modification is that of the greatly elongated
tongue, with its spoon-like tip adapted for reaching nectar of flowers
having deep-seated nectaries. For the same purpose, the mouth parts
are modified in a moth (Fig. 3) to form a long proboscis, which lies
curled up in a spiral beneath the head when not in use; in this case
the proboscis is the modified accessory jaws, the remaining mouth
parts, with the exception of the well-developed palps of the lower lip,
being greatly reduced. In a blood-sucking insect, such as the female
mosquito, all the mouth parts are well developed, but are very delicate
and greatly lengthened and suited for piercing the skin. The greatest
modification is found in the blow-fly proboscis, which is a soft,
sucking tube, with no outward resemblance to the generalised plan,
except for the palps of the accessory jaws. The mouth parts of insects
(_e.g._, aphids) which feed on the nutrient sap of plants, just in
the same way as mosquitoes do on blood, are modified for puncturing
the tissues of plants; in such insects the upper lip is short, and
both pairs of palps are atrophied, but the jaws and accessory jaws are
greatly lengthened in the form of bristle-like stylets, which lie in
a groove along the equally lengthened lower lip (Fig. 3). The manner
in which insects feed is of great importance in controlling them with
insecticides, and the two types to bear in mind are those that chew
their food and those that suck the sap of plants, reached by puncturing
the tissues.
As already stated, the thorax consists of the three segments
immediately behind the head, and carries the organs of locomotion; its
three segments are distinct, and may be referred to, respectively, as
the fore, middle, and hind thorax. The cuticle of each thoracic segment
consists of a number of chitinised plates connected by membranous
areas; these plates are arranged in three series--the back or dorsal;
the lower or ventral, forming the sternum; and the lateral, or
side-pieces, connecting the dorsal and ventral ones.
At the lower surface of each thoracic segment is attached a pair of
legs, the members of each pair being separated by the sternum of the
segment to which they belong. The presence of three pairs of legs is a
character by which insects can be distinguished from all other animals;
indeed, on account of this feature, insects are sometimes called the
hexapods, or six-legged animals. Each leg is covered by a continuation
of the body cuticle, and is five-jointed; the first two joints at the
attachment to the body are small; the next two are long, and form
the greater part of the limb; while the fifth, or foot, consists of
a varying number of small joints, the terminal one bearing a pair of
claws.
In the typical winged insects there are two pairs of wings: one pair
attached to the middle thorax, and the other to the hind thorax; owing
to the development of muscles controlling flight, the middle and hind
thorax of winged insects are usually better developed than the fore
thorax; this is especially noticeable in the thorax of two-winged flies
(daddy-long-legs and blow-flies), where the hind wings are reduced to
vestiges, the power of flight being thus confined to the middle thorax,
which forms by far the greater portion of the whole thorax.
Each wing, arising from the junction of the dorsal and lateral thoracic
plates, is a bag-like extension of the cuticle, flattened leaf-like, so
as to form a double flexible membrane. The wing membrane is supported
by several ribs or veins, which may be very numerous (grasshopper) or
few (aphid), while the fore edge, where it cuts the air in flight, is
bordered by a stouter vein, ensuring rigidity. The fore and hind wings
of some insects work independently, but in agreement of movement, while
in others the fore and hind wings of each side are coupled along their
adjoining margins, giving greater rigidity during flight.
The abdomen of insects consists of a varying number of visible
segments; each segment is covered by an upper and lower chitinous plate
connected by membrane, there being no side plates as are found in
the thorax. There are no organs of locomotion (except in a very few
cases), the only appendages being those connected with reproduction;
the latter are well developed in the female weta, where the egg-laying
apparatus, or ovipositor, projects blade-like from the apex of the
abdomen. In very many insects, however, the external reproductive
organs are not readily seen without special study.
All insects, from the largest to the most minute, contain internally
a well-formed heart and a digestive, reproductive, respiratory, and
nervous system (Fig. 3), while the spaces surrounding these organs
are, for the most part, packed with a complex system of muscles. The
heart is a delicate tube lying along the middle of the back or dorsal
surface of the body, immediately under the skin, and extends almost
from one end of the insect to the other; in an almost similar position,
close to the lower or ventral surface of the body, the nervous system
is situated, and consists of a chain of nerve centres, or ganglia,
connected by a double nerve cord, the most anterior of these ganglia
being in the head and forming the brain, the following three lying in
the thorax, one to each segment, while the remainder are confined to
the abdomen, one ganglion to each segment, as in the thorax. In many
insects the number of nerve centres is reduced, owing to the fusion of
two or more. The reproductive organs are located in the abdomen.
The digestive system consists of a tube (Fig. 3), with its appendages,
opening at the mouth and at the posterior end of the body; this
alimentary canal may be straight and simple, or convoluted and complex,
according to the insect and the nature of its food. Respiration in
insects is carried on by means of a system of air tubes (Fig. 3), which
branch and re-branch to form an intricate system of delicate tubular
airways, carrying the atmosphere to all tissues of the body; the main
air tubes open at the surface by a series of breathing pores normally
arranged along each side of the body, except on the head; these pores
are best seen on a caterpillar or on the abdomen of adult insects.
CHAPTER IV.
Life Histories of Insects.
No doubt owing to the endless assortment of sizes, from mere specks to
giants of a few inches, a widespread idea has arisen, particularly in
regard to such insects as have a general resemblance to one another,
that the smaller individuals are the younger stages of the larger.
Though gradation in size may be a sign of successive ages in certain
insects, the presence of functioning wings denotes that growth has
ceased; in the case of wingless insects, the characters of maturity
may be less conspicuous. Although there may be at times a fairly wide
range in size among fully-grown individuals of the one species, such
variation is not due to age, but to certain factors influencing the
insect during growth, such as the abundance or scarcity of food supply,
and favourable or unfavourable climatic conditions. On the other
hand, the sex to which an individual belongs is often responsible for
difference in size, males very frequently being smaller than females.
Size, therefore, is by no means a sign of age, and the smaller winged
insects must not be regarded as the young of the larger ones, no matter
how close is the resemblance.
Insects, with the exception of certain species giving birth to
living young, are reproduced from eggs laid by the females; with few
exceptions, the latter take no further interest in the eggs beyond
placing them in surroundings offering the most favourable conditions
for their well-being, and a sufficient food supply for the forthcoming
young; each egg is protected by a delicate shell, through which the
young insect makes its way on hatching.
On emerging from the egg, the young insect commences to feed and grow
in size, until very soon a stage is reached when the cuticle or shell
becomes too small for the enclosed insect; a fluid then collects
between the cuticle and the underlying skin, and a new and more roomy
cuticle is secreted by the latter; on this process being completed,
the old chitinous covering splits, and the insect withdraws itself.
This moulting takes place several times, until the body is fully grown,
when the cuticle formed at the last moult is retained by the now adult
insect for the rest of its life.
The different stages through which an insect passes from egg to adult
constitute its life history, or life cycle, and the relation of the
latter to the seasons, its seasonal history. According to the species,
a full twelve months or even more may be necessary for the complete
life cycle, or the cycle may be repeated several times within the year;
when the cycle occupies twelve months, the insect is single-brooded;
but two, three, or four-brooded, etc., when the cycle is repeated
two, three, or four times, respectively, in the year. Climatic and
food-supply conditions have a distinct influence on the number of
broods, the one species in many cases being single-brooded in colder,
and two or three-brooded in warmer climates. During the winter, when
the temperature is low enough, insects are more or less dormant in some
stage of their life cycle; such a state is the period of hibernation.
[Illustration: FIGURE 4.
1, Silverfish. 2, Earwig; a, young larva; b-d, later stages; e, adult.
3, Cicada; f, young larva; g, resting stage prior to emergence of
adult; h, adult. 4, Thrips; i and j, larvae; k, first stage pupa; l,
second stage pupa; m, adult. 5, Aphis-lion; n, larva; o, pupa; p,
adult. 6, Moth; q, egg; r-t, larvae; u, pupa; v, adult. 7, House-fly;
w, egg; x-z, larvae; aa, puparium; bb, adult. NOTE: Developing wings
shown in black.]
All insects do not follow the same method of development from egg to
adult, and the adaptations of structure and habit are many and varied
as well as simple and complex. Species having a complex development,
during which they pass through stages, each differing in form from its
predecessor, undergo what is known as a metamorphosis; contrasted with
such insects are those developing in a simple manner without pronounced
differences in the form of successive stages, the young resembling the
adult in most features except size and maturity--these insects are
without a metamorphosis. Intermediate between these two extremes are
other insects with a partial metamorphosis.
A consideration of the life cycle of some common insects will serve to
illustrate the principles of development discussed above. Firstly, will
be taken examples of complex development or complete metamorphosis;
secondly, examples of simple development or absence of metamorphosis,
followed by a review of species having a partial metamorphosis, thus
linking the first two types.
A convenient type of insect undergoing a complete metamorphosis is any
common moth (Fig. 4); one of the most suitable, most easily obtained
in all stages and commonest in any part of the country from spring to
autumn, is the magpie moth (_Nyctemera annulata_) and its caterpillar,
the “woolly bear.” The moth, unlike most of its kind, is a day-flying
species, and is very conspicuous owing to its black colour relieved by
white wing spots, and orange-yellow bands on the abdomen; the equally
conspicuous caterpillar, feeding on groundsel, ragwort and cineraria,
is black, with a very hairy body marked with narrow brick-red lines.
The eggs are laid in clusters by the female moth on the under side
of the leaves of the caterpillars’ food-plant; at first the eggs are
of a pale green colour, but assume a darker yellowish tint within a
few hours, and finally a leaden colour some time later. These colour
changes are due to the developing embryo, and just before the young
insect (the caterpillar in this case) hatches, its outline as it lies
curled within the egg is easily seen through the transparent egg-shell;
near the top of the egg is a black spot marking the position of the
caterpillar’s head, while the numerous delicate black lines below the
egg surface are the black hairs with which the caterpillar is clothed.
According to temperature and humidity, the incubation period--that
is, the period between egg-laying and the hatching of the young
caterpillar--varies from eight days to three weeks. The process of
hatching occupies about two hours, the young insect using its jaws to
eat an exit hole through the egg. The caterpillar stage--indeed, the
first stage of all insects--is known as the larva.
At first the larva of the magpie moth, measuring about one-sixteenth
of an inch long, is pale yellow in colour, except for the black head
and hairs clothing the body; very soon, however, the body becomes
characteristically black, and develops the reddish lines. During growth
the larva feeds continuously day and night, undergoing from five to ten
moults before becoming fully grown. During a moult the cuticle of the
head is cast separately from that of the body.
The body of the larva is worm-like, not only in general form, but
also in its segmented appearance; it is, however, a very different
animal from a worm. The larva has a distinct head, a pair of eyes, and
short antennæ, and a set of mouth parts, similar to those of the weta
or grasshopper, well adapted for devouring foliage; the first three
segments behind the head correspond to the thorax of the moth, and each
bears a pair of short feet; the remaining segments are those of the
abdomen, and have no true feet, but six pairs of sucker-like appendages
called pro-legs. The number of pro-legs varies from four to six pairs,
according to the species of moth, and are found only on the larva.
The time occupied by larval development of the magpie moth varies from
forty to eighty days in summer and autumn; but if winter intervenes,
causing the larvæ to hibernate before completing their development,
the larval period may be as long as two hundred and forty-eight days;
normally this insect hibernates in the larval state, completing its
development during the following spring. Throughout winter the larvæ
hibernate singly or in colonies under loose bark, in leaf axils, or any
suitable crevice.
The fully-grown larva measures about one and a-half inches long.
Prior to the final moult it ceases to feed, and wanders in search of
a suitable place in which to undergo the next transformation, usually
among stones, rubbish, or under loose bark, etc. There it spins a
white silken cocoon, among the strands of which are entangled the long
black body hairs; herein the larva undergoes the final moult, the cast
cuticle being easily seen at one end inside the cocoon.
The insect, however, has now assumed a form quite different from
that of the larva; this form is the chrysalis or pupa, and as such
is incapable of locomotion and feeding. The pupa measures about
three-quarters of an inch long, is yellowish at first, but soon becomes
black with yellow markings, while the form of the future moth (head,
antennæ, thorax, legs, wings and abdomen) can be traced on the pupal
cuticle. After from about two to five weeks, the pupa opens by a
cross-shaped slit on the back just behind the head, and the moth draws
itself out. At first the moth is comparatively helpless after having
been confined within the limited space of the pupal cuticle; soon,
however, the body hardens, the wings smooth out, and the insect is
ready for flight.
Metamorphosis is carried to a much higher state of perfection in the
case of such insects as blowflies and houseflies (Fig. 4). The larva,
or maggot, is without any external sign of head and legs, though these,
together with the wings of the future fly, develop from rudiments
within the body of the maggot. At the final moult the larval cuticle
is not discarded, as in the case of the moth, but hardens to form a
case--the puparium--within which the pupa lies.
The life-cycle of the magpie moth is illustrative of the principles of
metamorphosis characterising the development of a great many insects,
such as all moths and butterflies, beetles, flies, bees and wasps,
etc.; but, although the general characters of the larva, pupa, and
adult moth are common, with but slight variation, to corresponding
stages of moths and butterflies as a whole, these stages in other
insects, though readily recognised, have their own characteristics.
Outstanding features in a life-cycle involving metamorphosis are that
growth takes place only in the larval state, and that the insect
parades through life in different guises--egg, larva, pupa, and
adult--each with its own peculiarity of habit and form, although the
adult and pupa resemble one another much more than do the adult and
larva; but no matter how dissimilar the larva, pupa, and adult may
outwardly seem, structures common to them all may be traced throughout.
Make, for example, a comparative study of the larva, pupa, and moth
of the magpie moth; the head, thorax, and abdomen can be seen in each
stage, while counterparts of the larval antennæ, eyes, mouth-parts
and feet persist in the moth, though more or less profoundly modified
during pupal transformation. Although there are no external signs of
wings in the larva, these appendages are developing, nevertheless,
in concealed “pockets” within the larval thorax, and, at the time of
pupal formation, become extruded and lie ensheathed with the legs and
antennæ in the pupal cuticle along the sides of the pupal body. Apart
from these changes, the larval mouth parts undergo a most profound
metamorphosis; apparently, though there is no similarity between the
long “tongue” or proboscis of the moth and the jaws and accessory jaws
of the caterpillar, the proboscis, adapted for sipping the nectar of
flowers, is nothing but the accessory jaws of the leaf-chewing larva
greatly elongated; with the exception of the palps of the accessory
jaws, the other larval mouth parts are either absent in the moth or
reduced to vestiges.
In the case of insects that develop without a metamorphosis, the
life-cycle is one of comparative simplicity. An example of such an
insect is the so-called “silverfish” (_Lepisma saccharina_), common in
dwellings, especially in damp places, dark and dusty corners, flour and
sugar bins, while not uncommonly it causes some considerable damage
by devouring the paste and glaze from wallpapers and the binding and
leaves of books.
The silverfish (Fig. 4), wingless throughout life, measures about
one-quarter of an inch long when full grown; it is silver-white in
colour, due to a clothing of glistening scales that rub off as a silky
powder when the insect is handled. It glides rapidly about, especially
after dark, and is one of the most primitive insects, there being
minute leg-like processes attached in pairs to the under side of the
abdomen; the normal thoracic legs are well developed. The body is
wedge-shaped, tapering to the posterior end, from which three tail-like
appendages project, while anteriorly a pair of long, delicate antennæ
arises from the head.
All stages of the silverfish, from the minute, freshly-hatched
individuals to fully-grown ones, may be found in the one place, the
smaller ones being immature developing stages. In the case of another
species allied to the common silverfish, the female lays from six
to ten eggs at one time in sheltered crevices, and the young hatch
forty-five to sixty days later, when the temperature ranges from 65
degrees to 68 degrees Fahrenheit.
Unlike the moth larva, that of the silverfish throughout its growth
resembles the adult both in habit and form, the only marked differences
being that of size and the absence of the abdominal leg-like
appendages. During growth several moults take place, and at the final
one the adult appears with all its characteristics. Some species
take two years to reach maturity. In this type of insect there is,
therefore, no pupal or resting stage, and the larval habits and food
are the same as those of the adult insect, while there is but little
difference in structure throughout all the stages.
There are many winged insects (_e.g._, cockroaches, crickets and
earwigs) that show a slight advance toward a metamorphosis. Though
their larvæ differ from the adults principally in the absence of wings,
there are stages between the younger larvæ and the adults in which
the wing rudiments appear. These rudiments first appear after one of
the moults as small bud-like structures on each side of the thorax
(earwig, Fig. 4), becoming larger after each succeeding moult, when
the developing wings may be seen enclosed in a sheath of the cuticle;
at the final moult the wings, no longer enclosed in their coverings,
straighten out and become functional. A very pronounced difference is
here noted between the wing development of such insects and that of a
moth, in that the wing rudiments of the former develop externally and
those of the latter internally.
A decided advance toward a metamorphosis is exhibited by insects
known as thrips (Fig. 4). Though readily overlooked on account of
their minute size (one-twenty-fourth of an inch and less), they are
nevertheless conspicuous on green foliage and white flowers owing
to their blackish or yellowish colour. Thrips, when magnified, are
easily recognised by their peculiar wings; each is feather-like, being
formed of a narrow rib-like membrane clothed along the margins with
long and delicate stiff hairs. Thrips’ eggs are laid upon the plant
surface or within the tissues, according to the species, and are very
minute (about one-twenty-third of an inch long). The larvæ puncture
the plant tissues and feed upon the juices just as do the parents,
which they resemble in general form, except that there are no wings and
the antennæ are very short and the eyes small. There are two or three
larval moults, after which the insect is more like the adult, though
still resembling the larva. It now differs from the latter, however,
in the antennæ being considerably shortened, and in the appearance of
a pair of finger-like processes on each side of the body attached to
the thorax and lying along the sides of the abdomen; these processes
are the sheaths enclosing the wing rudiments of the future adult. The
insect again moults, changing to a form resembling the preceding stage
in many respects, but differing in the wing sheaths being much longer,
and in having the antennæ, enclosed in sheaths of cuticle, turned back
over the head. Although during these two stages the insect is capable
of moving about, it is nevertheless sluggish and does not feed; from
this second semi-quiescent stage the adult emerges. In the thrip’s
cycle, therefore, although the habits of the larva and adult are
similar, the presence of the two intermediate semi-quiescent stages,
during which feeding ceases, shows a decided advance toward a true
metamorphosis and represents a pupal stage.
In the case of those insects not involved by a metamorphosis, as
discussed above, the structure and habit of both adult and the immature
stages differ but little, the development of wings being the principal
change, except in the case of the thrips, where there is a definite
tendency toward a pupa. However, passing on to a consideration of the
common cicada (wrongly called a locust), a change in both structure and
habit occurs during the life-cycle, the immature stages being adapted
to a subterranean life, while the winged adult frequents the foliage
of trees; all stages agree, however, in puncturing plant tissues with
their proboscis and sucking up the nutrient juices from the roots by
the larva and from the stems and leaves by the adult.
The female cicada (Fig. 4) lays its eggs in colonies beneath the young
bark of trees and shrubs; the larvæ, on hatching, drop to the ground,
into which they burrow; the antennæ and soft body are comparatively
long, while the fore legs are greatly modified for grasping plant roots
and as digging tools. After a number of moults, the body shortens,
the antennæ come to resemble those of the adult, and the rudiments of
the wings appear. Growth and the activities of the developing insect
continue until finally the larva constructs an earthen underground
chamber, in which it lies torpid until ready to undergo the final
moult; in this inactive state, though still resembling the later larval
stages, the insect corresponds to the pupa of the moth. For the final
moult the pupa leaves the ground, crawls up some support (a tree trunk
or post), where the winged adult emerges, leaving the empty pupal husk
attached to the support. Besides the change in habit and the possession
of functional wings, the adult cicada differs in many structural
features from the immature stages. Outstanding differences are the
normal fore legs, the development of a “voice-box” in the male, and an
ovipositor in the female.
An insect that shows some linkage between those having a true
metamorphosis and those having a partial metamorphosis is the
aphis-lion (_Micromus tasmaniæ_), though undergoing a true
metamorphosis itself. The larvæ are predaceous and feed upon aphids
(Fig. 4). Its larva, pupa, and adult are distinct forms, as in the
moth, but the larva is not of the specialised caterpillar or grub type,
rather resembling in general appearance the silverfish, or the type of
young larva peculiar to such insects as the earwig or thrips before the
wing rudiments develop. Furthermore, the pupa, though one in the strict
sense, is capable of great freedom of movement, its head, mouth-parts,
antennæ, legs and wings, ensheathed by the cuticle, being freely
movable, and not rigidly attached to the body.
A review of the early larval stages of the earwig, thrips and cicada,
prior to wing development, and of the aphis-lion larva, shows a
conformity to a generalised type exemplified by the primitive
silverfish. On the other hand, the moth caterpillar exhibits another
larval type more highly specialised, though still retaining a modified
semblance to the silverfish type, while specialisation is carried to
the highest degree in the blowfly maggot, where all outward sign of
the primitive larval type is lost. Regarding the pupæ, there are three
types; the most simple is the free pupa, like that of the aphis-lion,
and some moths, beetles, etc., where the appendages are freely movable.
The most complex is the pupa of the blowfly, enclosed in its puparium,
while intermediate between these two extremes are many moth pupæ that
have the appendages firmly attached to the body, but nevertheless
visible.
CHAPTER V.
Sucking Insects.
The term “sucking insect” is applied to all insects that have the
mouth parts modified as delicate stylets, by means of which the plant
tissues are punctured and the nutrient sap sucked up. Not only may such
insects weaken the infested plants, but they also cause the destruction
of chlorophyll, interfere with the normal functioning of the stomata,
and have a toxic effect upon the tissues; further, many serious
plant diseases are carried and spread by sucking insects, whilst the
punctures made when feeding may allow the entry of disease spores.
Among sap-sucking insects are scale insects, mealy-bugs, aphids,
leaf-hoppers, white-flies, thrips, etc. Infestation by most of these
insects (especially in the case of scale insects, mealy-bugs, and
aphids) is very often detected by the sticky nature and blackened
appearance of the plants; this is due to the fact that the insects
excrete a sweet, sticky substance known as “honey-dew,” which collects
on the foliage and branches, whilst upon it grows a black, sooty mould.
Scale Insects and Mealy-bugs.
Scale insects and mealy-bugs, collectively known as coccids, are of
very great economic importance on account, not only of their widespread
depredations upon plants, few being free from infestation, but also of
the commercial value of some species--_e.g._, in the production of lac,
cochineal, Chinese wax, etc.; it is with the injurious forms that the
New Zealand horticulturist is concerned. The term “scale insects” is
derived from the appearance of many of the species that are protected
by a scale-like covering, which forms a conspicuous scaly incrustation
when a plant is heavily infested.
Of the several kinds of insects injurious to vegetation, the coccids as
a family are undoubtedly of major importance, because they infest not
one group, or allied group, of plants, as do so many other injurious
insects, but an extensive range of widely different plants. Some
coccids are much more injurious than others, the San José Scale, for
example, having a very virulent toxic influence, while the Greedy
Scale may cause but little damage, even when the plant is completely
encrusted by it; further, some plants may be more susceptible to injury
than others by the same species of coccid.
Coccids, as a whole, are highly specialised insects, and among
themselves exhibit a great variety of forms. Throughout the group
the sexes differ to a marked degree. The adult males, which vary
but little in all the coccids, are usually minute, and, with few
exceptions, two-winged (Fig. 5); none has mouth parts, these appendages
having become atrophied during metamorphosis, which is complete, while
many have one or more hair-like tail appendages. On the other hand,
females are never winged; some are comparatively large; all have
well-developed mouth parts throughout life, and undergo incomplete
metamorphosis, while in many forms the legs and antennæ are lost before
maturity.
In all cases coccids secrete a protective covering, which assumes
different forms; this fact, together with the chief methods of female
development, is utilised for the purpose of this work to arrange the
coccids under three main types as follows:--
1. LESS SPECIALISED FORMS.--Examples are the mealy-bugs and
cottony-cushion scale, which belong to the more generalised or least
specialised representatives. The protective body covering is in the
form of a powdery or mealy secretion; the legs and antennæ are retained
throughout life, and the insect remains freely mobile.
A typical-form life-cycle may be studied in that of the cottony-cushion
scale (Figs. 5 and 6a). During development the female insect passes
through three larval stages; each of these stages is, on the whole,
similar, except for size and minor structural changes, and the white
powdery secretion that covers the reddish body of the adult.
2. INTERMEDIATE FORMS.--An example is the olive scale (Fig. 5). In
such forms there is a tendency to specialisation, owing to more or
less sedentary habits in later life, and protection is afforded by a
thickening and toughening of the cuticle on the upper surface of the
body. Unlike the cottony-cushion scale, the female olive scale passes
through two larval stages; the minute first stage larva is active and
very flat; it soon settles upon a leaf and commences to feed, when it
becomes much flatter and a little larger; the second stage differs
from the first in size and in the development of a dorsal longitudinal
ridge, which eventually forms the cross-bar of the two transverse
ridges that are characteristic of the third or adult stage, when the
insect swells and assumes the shape of the mature form. After settling
in the first larval stage, the insect becomes very sluggish, and
does not move, except to migrate, as most do, from the leaves to the
twigs, there to take up a permanent position. The legs and antennæ are
retained throughout life, but in the adult are functionless, being
folded against the body; in some species of intermediate forms the
appendages become atrophied during development. In the olive scale, and
related forms, the toughened cuticle not only serves as a protection to
the insect, but also as a receptacle for the eggs (Fig. 5); as these
are laid and increase in numbers, the body of the parent diminishes and
is crowded against the dome-shaped cuticle.
3. SPECIALISED FORMS.--The apple mussel-scale (Figs. 5 and 7, Nos. 2
and 6) is a representative of this group, the members of which are
markedly specialised, the legs and antennæ of the adult female becoming
completely atrophied during development, and the shape of the body
profoundly altered; protection is afforded by a scale-like covering not
attached to the body. In the mussel-scale development there are two
larval stages: the first, like all coccids, has the legs and antennæ
well developed and is active.
[Illustration: FIG. 5.--ILLUSTRATIONS OF DIFFERENT TYPES OF
SCALE-INSECT LIFE-HISTORIES.]
On settling to feed, this first larva commences to produce a covering
of white threads that mat together to form the first scale; the second
stage larva presents profound changes in the absence of legs and
antennæ, while the body has become pear-shaped, the head, thorax and
abdomen seeming as one; a second more waxy scale is now formed. After a
second moult, the adult appears, and resembles the second stage larva
in form; the adult constructs a third scale, very much larger than the
earlier ones, to which it remains attached by its anterior end.
Though many of the specialised coccids form elongate scales, as in the
case of the mussel-scale, numerous others construct circular scales, as
does the San José (Fig. 5); in the latter, the second and third scales
are constructed round the first, so that the first and second appear
as pimple-like structures in the centre, or slightly to one side of
the completed covering. As with the olive scale, the covering of the
specialised forms serves as a receptacle for the eggs (Fig. 5).
Some of the more important coccids occurring in New Zealand will now be
discussed.
COTTONY CUSHION SCALE(_Icerya purchasi_).--This insect (Fig. 6a) is
a native of Australia, but has now become established in many other
countries, including New Zealand. For a time it was a serious pest of
citrus, until the introduction and establishment of its natural enemy,
the ladybird beetle (_Novius cardinalis_).
The adult female is more or less oval, and covered with a yellowish
powder, partly concealing the reddish-brown ground colour and dark
spots along the sides of the body; the legs are black. A characteristic
feature is the white corrugated egg-sac attached to the end of the body
(Fig. 5). As the eggs are laid, this sac increases in size, until it
may measure fully 2-1/2 times the length of the parent, which becomes
tilted up. The eggs are orange-yellow, and as many as 800 may be
produced by a single female. The eggs hatch in about a fortnight during
summer, and the period of development to the adult ranges from three to
five months. The larvæ most frequently congregate along the mid-ribs
of leaves, and as development advances they usually migrate to the
twigs and branches. There are two generations each year. A considerable
variety of plants is attacked by this insect, chief among which are
citrus, acacia, gorse, wattle, and Douglas fir.
Control is effected by the agency of the ladybird, but epidemics
sometimes occur with which the beetle cannot immediately cope; in such
a case fumigation in the glass-house, or spraying with red oil in the
open, should be resorted to.
MEALY BUGS.--Mealy bugs are characterised in the female by the nature
of the waxy protective secretion which forms a powdery meal-like
covering over the body, but is developed as a fringe of leg-like
processes at the side (Fig. 6b); these processes at the posterior
end of the insect may be prolonged as longer or shorter tail-like
appendages in some species, or they may be no longer than those
fringing the body margins in others. Immediately after each moult the
larvæ are devoid of mealy covering and lateral processes, which are
secreted anew each time the cuticle is shed. In a mealy bug colony are
numerous small, narrow cocoons, in each of which a developing male
insect lies.
Most mealy bugs produce eggs, which are laid in a spacious, cottony sac
secreted at the posterior end of the female; the female insects, egg
sacs, and male cocoons together form characteristic woolly masses on
infested plants.
The injury caused by mealy bugs may be considerable, not only through
the drainage of plant sap, but also owing to the production of
honey-dew and its consequent sooty mould. All parts of plants are
subject to mealy bug attack, and the insects are frequently attended by
ants.
[Illustration: FIG. 6.
(a) Cottony cushion scale. (b) Mealy bug. (c) The black olive scale.
(d) Gum tree scale: On right, females on twig; upper left, male scales;
lower left, the ladybird beetle; centre, scales destroyed by beetle.
(e) Hemispherical scale. (f) Fruit lecanium scale.
_Photographs by W. C. Davies, Cawthron Institute._]
Mealy bugs are controlled to a great extent by natural enemies, among
which are the Tasmanian lace wing (_Micromus tasmaniæ_) and the
Cryptolæmus ladybird (_Cryptolæmus montrouzieri_), but the influence of
these is insufficient for commercial purposes. Attempts are now being
made at the Cawthron Institute, Nelson, to establish other parasites
recently imported from California.
Control under glass is effective by means of fumigation, but in the
open is a more difficult matter, though red oil and lime-sulphur give
some satisfactory results, together with the practice of removing rough
bark on trees where the insects hibernate. In New Zealand are several
species of mealy bugs, of which the following are of interest to the
horticulturist:--
LONG-TAILED MEALY BUG(_Pseudococcus adonidum_).--This species is
readily recognised by the long tail-like appendages of the female.
It is widely distributed and commonly met with under glass, where
it infests almost any plant; in the warmer and moister districts of
the Dominion it occurs out of doors. Its list of host plants is a
lengthy one, and includes grape vine, passion vine, wistaria, fig,
oleander, Phormium, cineraria, begonia, apple, plum, palms, ferns, etc.
Considerable injury may be caused by the insect when it occurs in dense
masses on the under side of foliage and upon young, succulent growth.
No eggs are produced by this insect, the young being born alive; the
production of young lasts for a period of from two to three weeks at
the rate of about twelve each day; the time taken to reach maturity
varies considerably, according to climatic conditions, the range being
from one to three months. There are comparatively few generations each
year out of doors, but under glass there may be several.
CITROPHILUS MEALY BUG(_Pseudococcus gahani_).--In New Zealand this
species is met with on grape vines and begonia in glass-houses, where
it becomes epidemic if left uncontrolled; out of doors it infests apple
and potato, and no doubt other plants are attacked. It is characterised
by the mealy covering being coarse and distributed unevenly over
the body, while the marginal fringe is short, the processes being
comparatively thick, particularly the tail-like ones, which are much
shorter than the body, though conspicuous.
Egg-laying covers a period of about two weeks, from 394 to 679 eggs
being deposited by each female; development to the adult is completed
in about six weeks, though this will vary according to the conditions.
In California four generations in the year have been noted.
APPLE MEALY BUGS(_Pseudococcus maritimus_ and _P. comstocki_).--Both
these species occur upon apple, pear and potato in New Zealand, the
former species originating in America, and the latter in Japan; the
injury to the host itself is not severe, but the presence of these
insects on the fruit is responsible for apples and pears being rejected
for export.
Both species are very similar in appearance, and are of the
short-tailed type; they differ from the citrophilus mealy bug in having
the mealy covering evenly distributed over the body, while the marginal
fringe is delicate and thread-like. The eggs hatch in from one to three
weeks, and the larvæ migrate freely, the insects reaching maturity one
or two months later, according to climatic conditions. In the open the
winter is passed in the egg stage, but under glass or in mild climates
activity among the different stages occurs throughout the year.
Apart from apple and pear, these insects have been recorded from many
plants: Baker’s mealy bug (_maritimus_) on lemon, orange, walnut,
willow, elder, ivy, iris; and Comstock’s mealy bug on citrus, elder,
euonymus, gooseberry, grape, horse chestnut, hydrangea, mulberry,
peach, persimmon, plum, poplar, wistaria.
THE GUM SCALE(_Eriococcus coriaceus_).--This is one of the most
spectacularly destructive scale insects now established in the
Dominion. It is a native of Australia, and its normal hosts are the
several species of eucalyptus, though it is sometimes found on apricot
and willow. A characteristic feature of infected eucalyptus is their
blackened appearance, due to sooty mould growing on the copious
honey-dew secreted by the scale.
On an infested twig or branch, the insects may be so closely packed
as to conceal the bark (Fig. 6, d); each female lies in a pear-shaped
sac of felted secretion, reddish-brown, tawny, or sometimes white
in colour, measuring about three-twenty-fifths of an inch long, and
having a circular aperture at one end. The enclosed insect is somewhat
flattened, oval, and blood-red in colour; when crushed, it leaves a
reddish and sticky smear. The developing males are to be found forming
white patches of innumerable individuals on the tree trunks under the
loose bark (Fig. 6, d).
The female is viviparous; during spring, mid-summer and autumn immense
numbers of young are produced, which escape through the opening at one
end of the female sac, and are carried long distances by the wind.
These young insects first settle on the eucalypt leaves, whence they
migrate, the females to take up their final position on the twigs and
smaller branches, and the males to continue their development on the
trunk of the tree.
The gum tree scale occurs throughout the districts east of the Southern
Alps and in the vicinity of Nelson, in the South Island, and over the
southern half of the North Island; it is, however, spreading rapidly
northward.
This pest is held in control by means of the black-ladybird beetle
(_Rhizobius ventralis_)--Fig. 6, d--which was imported for the purpose
from Australia; birds such as the tui, wax-eye, fantail, blackbird and
thrush congregate on infested trees and eat the insect.
OLIVE SCALE(_Saissetia oleæ_).--This insect has a world-wide
distribution, and is one of the most important pests of citrus in New
Zealand, although it occurs on a wide range of plants; in all cases it
infests the fruit, bark, and the under side of leaves. The host plants
include citrus, apple, pear, apricot, plum, almond, fig, grape-vine,
wistaria, pepper tree, oleander, holly, laurel, palms, camellia, rose.
The injury caused by the insect is not so much on account of its
weakening influence upon the infested plants as of the fact that it
copiously secretes honey-dew, so that black mould develops to a marked
degree, necessitating the washing of herbaceous plants and fruit.
The adult female (Fig. 6, c) is hemispherical, and measures about
one-fifth of an inch in diameter, a characteristic distinguishing
feature being the three ridges forming the letter H on its upper
surface (Fig. 5). According to age, the colour varies from brownish or
greyish to jet black, the insect being conspicuous against the lighter
background of bark or leaf; the small, immature individuals are light
brown or yellowish, and almost flat.
In New Zealand the winter is passed in both egg and larval stages,
though a few adults may be found at that time; on turning over what
appears to be an adult, it will usually be found that the female has
died and her place taken by numerous eggs (Fig. 5). The average number
of eggs produced has been estimated at from 1,500 to 2,000 per female;
at first the eggs are white, but prior to hatching they turn a deep
orange-red. Development is slow, the adult state being reached about
three months after time of hatching; egg laying commences about five
weeks after maturity, and continues for a period of about six weeks.
There is only one generation each year, and all stages may be met
with on the one plant; the greatest activity occurs during the summer
months. An important natural enemy of this scale is the steel-blue
ladybird beetle (_Orcus chalybæus_), introduced from Australia.
HEMISPHERICAL SCALE(_Saissetia hemispherica_).--This world-wide species
is commonly met with in New Zealand, and, though not a serious pest,
has a wide range of host plants, both in the open and under glass;
some of the commoner hosts are citrus, fig, oleander, palms, japonica,
camellia, asparagus, and orchids.
Both leaves and stems are infested by the insect, which resembles the
olive scale (Fig. 6, e); from the latter it may be distinguished by
its light brown colour and smooth surface, there being no ridges; the
longest diameter of the adult female is one-seventh of an inch. Between
500 and 1,000 eggs are laid by each female, and the life-cycle is
completed in about six months; the young insects settle along the main
leaf-veins.
TURTLE SCALE(_Coccus hesperidum_).--This widely-distributed insect,
though common in hot-houses and out of doors in the warmer parts of the
Dominion, is not especially injurious, except for the copious honey-dew
secreted and the consequent sooty mould; it occurs on holly, ivy,
camellia, citrus, laurel, myrtle, oleander, and japonica.
The insect infests leaves and stems, and is especially abundant on
succulent growth. The adult female is rather reddish-brown in colour,
dome-shaped, but with the margins flattened on the host plant; on
each side the margin is notched by a shallow depression, and there
is a deeper one at one end; over the surface is a reticulation of
ridges, resembling the pattern on the back of a turtle; fully-developed
individuals measure from one-sixth to one-eighth inch in diameter. This
species is viviparous, and development to the adult occupies about nine
weeks; there may be three or four generations each year.
FRUIT LECANIUM SCALE(_Eulecanium corni_).--This European insect is
common throughout the Dominion, where occasionally it becomes epidemic
and causes some temporary damage; with it are associated honey-dew and
sooty mould. Among the plants infested are apricot, peach, nectarine,
plum, pear, grape-vine, wistaria, raspberry, mulberry, blackberry,
gooseberry, black currant, ferns.
Leaves and bark are infested, and a narrow twig may be partly encircled
by the margins of the scale. The adult female (Fig. 6f) is oval and
dome-shaped, some individuals measuring one-sixth of an inch in length;
the surface is smooth, except toward the margins, parallel to which
are some wrinkles. The general colour is dark brown, but just prior to
egg-laying there are numerous transverse and longitudinal markings of a
lighter colour over the surface. The winter is passed in the egg stage
or as partly-grown young.
Another, but larger, species, closely resembling the preceding,
and found on grape-vines, wistaria, eleagnus, etc., is _Eulecanium
berberidis_. It is reddish-brown in colour, and measures up to
one-third of an inch in length.
GOLDEN OAK SCALE(_Asterolecanium variolosum_).--This insect is very
common upon English oak trees in parts of New Zealand. In many cases so
badly are the trees infested, that they become sickly in appearance,
and at times the greater part, or even the whole, of the tree is killed
through the agency of the pest.
The individual scale (Fig. 7, 1) is more or less circular, and about
one-sixteenth of an inch in diameter; it is of a greenish-yellow
colour, with a narrow paler circumference, though some, with the
exception of the rim, are partly or wholly brownish. Each scale forms
and lies in a depression of the bark. The insect is viviparous. A
minute parasite, _Habrolepis dalmanni_ (note the exit holes made by
the parasite during emergence from some of the scales shown in the
photograph) has recently been established as a means of control and is
proving effective.
CAMELLIA SCALE(_Pulvinaria camelicola_).--This European scale sometimes
heavily infests camellias and euonymus in New Zealand, but is not a
very serious pest, though more so in glass-houses than out of doors.
After the female has produced her eggs, she drops off the plant, so
that, though the latter shows evidence of injury, there may be no sign
of the insect.
The adult female is oval and about one-third of an inch at its longest
length; in shape it resembles a rather flattened turtle scale, but when
laying eggs the body shrivels and numerous transverse wrinkles develop,
although the margins of the scale remain smooth. There is at least one
generation each year, and in warmer parts probably a second, which may
reach maturity before winter or not till the following spring. The eggs
are laid in an elongate, white, cottony sac secreted at one end of the
female; this sac is sometimes as much as four to five times the length
of the insect. The eggs continue to hatch over a period of from four to
six weeks, and the larvæ rapidly spread; the latter settle along the
leaf mid-rib, margin, or lower surface.
APPLE MUSSEL SCALE(_Lepidosaphes ulmi_).--The apple mussel scale is
now established throughout the temperate regions of the world. It is
commonly met with on apple, but has a long list of host plants, among
which are pear, hawthorn, willow, poplar, gooseberry, and currant.
The insect (Fig. 7, Nos. 2 and 6) forms incrustations on bark and
fruit, and is commonly met with at the stalk end of the apple; the
individual scale is chocolate-brown in colour, is shaped like the shell
of the salt water mussel--hence the name “mussel scale”--and when full
grown measures one-eighth of an inch long.
A single female is capable of laying up to 700 eggs, in which stage the
winter is passed. The eggs hatch in the spring, and the young insects
swarm over the host plant in search of a suitable place to settle.
A continuous warm spell of weather in the spring will allow all the
eggs to hatch almost at one time, but alternating cold spells will
retard development, so that emergences take place over a longer period.
After emerging from the egg until maturity, when egg-laying again
takes place, a period of three months elapses; the insect is a slow
breeder, and produces only one brood a year in colder climates, but is
two-brooded in warm districts, such as Auckland.
A small hymenopterous parasite (_Aphelinus mytilaspidis_), less than
one-twenty-fifth of an inch long, attacks this scale, but does not
serve as an efficient control; individual scales that have been killed
by the parasite show a small hole through which the adult parasite has
emerged. The most effective control is secured by treating infested
trees with red oil or lime-sulphur during winter.
CABBAGE TREE SCALES(_Leucaspis cordylinidis_ and _Leucaspis
stricta_).--Cabbage trees and also New Zealand flax often have the
leaves encrusted by the white masses of these two native scales. The
adult female of one species (_L. cordylinidis_) measures one-eighth
of an inch long, is very narrow and straight as a rule, and white in
colour, except for the yellow anterior end (Fig. 7, 4). The other
species (_L. stricta_) resembles the former, except that the adult is
one-eleventh of an inch long, and has the anterior half blackish. In
the case of ornamental cabbage trees and flax, control can be effected
by removing all dead and scale-infested leaves, thus allowing access to
sunlight.
SAN JOSÉ SCALE(_Aspidiotus perniciosus_).--Of all scale insects of
major importance, the San José (Fig. 7, 5) is outstanding, in that it
is one of the insects most destructive to deciduous trees and shrubs,
a considerable number of which are liable to attack. It is of Chinese
origin, and first came into prominence when it became established at
San José, in California, hence its name. Owing to its small size, it
is easily overlooked, except when epidemic, and is readily transported
upon plants from one country to another.
The list of plants attacked is a long one, but the following may be
mentioned:--Acacia, hawthorn, quince, privet, poplar, almond, apricot,
cherry, plum, peach, pear, apple, gooseberry, currant, roses, willow,
ash, elm.
The female San José scale is circular in outline, having a diameter
of about one-twenty-fifth of an inch; in profile it has the form
of a flat cone with a crater-like depression at the apex, in the
centre of which lies a minute pimple-like prominence; the immature
scales are smaller and whitish in colour, while the male scale is
elongate-oval in outline, with the crater-like depression toward one
end. The individual scales are greyish and are readily overlooked, but
when well established upon a tree they form an incrustation giving a
characteristic dull silver-grey appearance to the tree; bark, fruit
and leaves are infested. A characteristic feature of San José scale
infection is the discolouration of the plant tissues immediately
surrounding each insect, which turn a distinct red or purple, giving at
once an indication that this scale is present.
The winter is passed by the insect in almost a mature state; on the
advent of spring, development to maturity continues, when, after
mating, the females give birth to living young over a period of several
weeks. The young reach maturity and commence to reproduce five to six
weeks from birth, there being several generations in the course of a
season. The average number of young produced by each female has been
found to be about 400.
[Illustration: FIG. 7.
(1) Golden Oak Scale; (2) Apple Mussel Scale; (3) Black Scale; (4)
Cabbage Tree Scale; (5) San José Scale; (6) Apple Mussel Scale; (7)
Oleander Scale; (8) and (9) Rose Scale.
_Photographs by W. C. Davies, Cawthron Institute._]
Natural enemies in New Zealand are two species of hymenopterous
parasites, _Aphelinus fuscipennis_ and _A. mytilaspidis_, the latter
also attacking the apple mussel scale. Ladybird beetles also feed upon
the insect.
Control requires close attention, and can be effected by the
application of lime-sulphur in the dormant season, when it is essential
to apply a strong wash to kill off as many scales as possible before
reproduction commences in the spring. At bud movement further
applications are necessary to destroy the young insects.
RED ORANGE SCALE(_Chrysomphalus aurantii_).--The red orange scale
is distributed throughout the world, and is especially abundant in
tropical and sub-tropical regions, the most southern limit being New
Zealand. As a major pest it is peculiar to citrus, but infests to a
minor extent other plants--_e.g._, plum, apple, pear, quince, grape,
fig, euonymus and rose. So far it has been found only on citrus in
New Zealand, it being well established in the Auckland province, and
also in the South Island on Banks Peninsula. It is very often found on
imported oranges and lemons.
This scale is a circular one, with a central pimple-like prominence, as
in the case of the San José, but is flatter, about half as large again,
and is of a characteristic reddish colour. The damage done to citrus
trees by this insect is of a serious nature, as the entire tree or part
of it may be killed in severe infestations. A characteristic feature
of this species is that no honey-dew is secreted, and hence there is a
total absence of sooty mould on infested trees.
Like the San José scale, the red scale is viviparous, and over-winters
as partially mature adults, completing development in early spring,
when the young insects make their appearance. An average of about 55
young is produced by each female, and development to maturity takes
from two or two and a-half months; about one month later young are
produced, and their production continues over a period of one or two
months; climatic conditions, however, have a direct influence on
development.
An important natural enemy is the steel blue ladybird (_Orcus
chalybæus_), imported from Australia; but the most efficient control is
cyanide fumigation, or spraying with red oil or lime-sulphur.
THE BLACK SCALE(_Chrysomphalus rossi_).--Foliage of palms, oleander
and citrus is often infested by this reddish-black to black circular
scale (Fig. 7, 3); it is almost flat, with a central whitish spot, and
measures up to one-tenth of an inch in diameter; when many individuals
are crowded together, their outline becomes irregular. This species is
not especially injurious, though common.
OLEANDER SCALE(_Aspidiotus hederæ_).--This cosmopolitan insect occurs
on orchids, oleander, ivy, camellia, palms, citrus, coprosma, and
karaka, infesting stems, leaves and fruit. In the case of citrus, this
insect delays colouring of the fruit, which becomes blotched with
yellow or green. The insect may be so numerous, that it completely
covers the whole plant, giving to the latter a white appearance; this
is due to the preponderance of white male scales, the female being
slightly yellow, with a purplish tint.
The female scale is almost circular (Fig. 7, 7), having a diameter of
from one-twenty-fifth of an inch to two-twenty-fifths of an inch, and
is rather flat; the male is more oval and of the same size, and in both
cases there is a central orange-yellow spot. The eggs are comparatively
large, and hatch soon after being deposited. The insect reaches
maturity in from four to six weeks.
GREEDY SCALE(_Aspidiotus rapax_).--This European insect is now
widespread, and in New Zealand is common on apple, pear, quince, and
wattle; it has a wide range of hosts. The adult female scale is convex
and of a general grey colour, though sometimes yellowish. The winter is
passed in all stages of development.
ROSE SCALE(_Aulacaspis rosæ_).--This is a very common insect, forming
white incrustations on the bark of roses, briar, raspberry, loganberry,
blackberry, and sometimes pear. The adult female (Fig. 7, 8), which is
from one-twelfth of an inch to one-eighth of an inch in diameter, is
rather thin and flat, circular or oval in outline, but irregular when
crowded; the general colour is white or slightly yellowish. The male
(Fig. 7, 9) differs, in being elongated and narrow. This insect can
withstand severe winters, and is to be controlled by the use of red
oil.
CHAPTER VI.
Sucking Insects--(Concluded).
Plant Lice, or Aphides.
The small, soft-bodied plant-lice, or aphides, usually found forming
dense colonies on all sorts of plants, are pests well known to every
gardener; they attack plants by inserting into the tissues their
delicate piercing mouth-parts, and drain the nutrient sap (Fig. 8, 1g).
All parts of a plant may be infested, and the insects, owing to their
ability to reproduce abundantly and rapidly, may destroy the plant,
or at least injure it by stunting its growth, curling the leaves,
or deforming the flowers and fruit. In many cases aphides copiously
secrete honey-dew, upon which sooty mould grows, rendering the plant
unsightly; on this honey-dew ants feed, and are frequently seen
associated with aphides. Apart from their direct injurious effects,
aphides are of outstanding importance, in that they transmit some of
the most serious plant diseases. Of all the species occurring in New
Zealand, only one species is supposed to be a native.
Most aphides live exposed upon the host plant (_e.g._, Rose Aphis),
but some (_e.g._, Woolly Aphis) secrete a protective covering, while
others cause a malformation of the plant tissues which form a partial
protection as a semi-gall (_e.g._, Elm-leaf Aphis), or a complete
protection as a true gall (_e.g._, Leaf-petiole Gall-aphis of Poplar).
Aphides present certain variations in structure, and, generally
speaking, the one species presents four or five types (Fig. 8, 1): the
asexual (parthenogenetic) wingless and winged females that give birth
to living young (viviparous) in the absence of males, and the sexual
forms, both males and females, the latter producing eggs (oviparous).
The best character by which the New Zealand aphides are to be
recognised is to be found in the pair of longer or shorter horn-like
processes, or “cornicles,” projecting from the upper surface of the
abdomen; in some species, however, the “cornicles” are reduced and
inconspicuous (_e.g._, Woolly Aphis), or altogether absent (_e.g._,
Grape Phylloxera). The “cornicles” are frequently called “honey-tubes,”
since for many years it was thought that they secreted the honey-dew;
it has been shown, however, that the honey-dew is secreted from the
rectum, and that the function of the “cornicles” is to secrete a waxy
protective substance, which may take the form of a powder or woolly
threads. The wings, when present, are membranous, the front pair being
much larger than the hind ones, and when not in use usually close
roof-like over the body.
[Illustration: FIG. 8.
(1) Life History of an Aphis: A, egg; B, C, and F, wingless females;
D, winged female; E, male; G, section of head and plant tissue to show
method of attack. (2) Life History of a Leaf-Hopper: H, eggs under bark
of twig; I, first stage hopper; J, later stage hopper with developing
wings; K, adult from above; L, adult from side. (3) Life History of a
White Fly: M, egg; N, first stage larva; O, pupal stage under scale
covering; P, adult. (4) An adult Thrips.]
In their life-histories and habits aphides present many variations,
sometimes of considerable complexity, but fundamentally the processes
are as follows:--Eggs are laid on the host plant during the autumn,
and give rise to wingless females in the spring; these females
(being asexual or parthenogenetic, since they reproduce without
being fertilised) are viviparous, producing living forms similar to
themselves. Some of these forms remain wingless, while others may
develop wings, upon which a wider dispersal of the species depends,
but in both cases such females are asexual and viviparous. Several
such generations may develop until the autumn, when males and females
appear, the latter being oviparous, producing the over-wintering eggs
when fertilised by the males. Very often, however, the life-cycle is
considerably complicated by the winged forms flying to other host
plants and establishing there colonies differing in many respects
from the parent stock; from these secondary hosts there is a return
migration to the original species of plant. Again, the migrations may
be restricted to different parts of the same plant, from the leaves
or branches to the roots, for example. Most aphides are readily
controlled by means of insecticides, such as nicotine-sulphate, or
kerosene-emulsion. They are also very often held in check by natural
enemies, such as aphis-lions, hover-flies, ladybirds, and numerous
forms of hymenoptera. The following species are some of the commoner
aphides met with in New Zealand:--
BLACK PEACH--APHIS(_Aphis persicæ-niger_).--From early spring, even
before the foliage develops, this aphis may be found heavily infesting
the young, succulent shoots of peach; it also occurs on cherry, plum
and nectarine. The adult insects are black and the immature stages
pale reddish-brown, dull brown, or lemon-yellow. During the winter the
insect lies underground about the roots of the host plant, and thence
migrates to the young growth in spring. At first only wingless forms
are seen, but as the season advances the winged migratory aphides
develop; at that time the foliage is so severely attacked that it
becomes crumpled and functionless (Fig. 9, 1), while the developing
fruit is distorted and rendered useless. The heat of the late summer
destroys the aphides still on the foliage, but sufficient numbers
descend underground for protection, where they live over winter.
GREEN PEACH--APHIS(_Rhophalosiphum persicæ_).--This aphid occurs
on a wide range of plants, including the peach, and, as a rule, is
most abundant during summer and autumn; as the name implies, the
general colour is green, though some individuals are reddish or
brownish-yellow; the wingless forms have black-tipped “cornicles,” and
on the abdomen of the winged insects are dark markings.
BLACK CHERRY--APHIS OR FLY(_Myzus cerasi_).--This aphid has now a
world-wide distribution. In New Zealand it has been found on cherry
and plum, though in other countries its hosts include peaches, red
and black currants, and cruciferous plants, such as common mustard,
shepherd’s purse, etc. This species exudes copious honey-dew, upon
which sooty mould develops, thus rendering fruit unfit for use. The
principal injury, however, is due to the destruction of shoots and
leaves, the latter frequently curling up when the insect clusters in
dense colonies upon the infested plant. The complete life-cycle has
not been followed under New Zealand conditions, but the shiny black
eggs occur on the bark and buds of cherry trees during the winter. In
spring the eggs hatch, and the insects, rapidly reproducing, attack
the young shoots and leaves. Observers in other countries have noted
that there is a summer migration of winged females to cruciferous
plants, where colonies are established, and whence there is a return
migration during the autumn to the original host. The wingless females
are black, with part of the legs yellow, while the young individuals
are pale in colour; the winged females have a green abdomen, from which
arise the black “honey-tubes.” Since all the over-wintering eggs have
hatched by the time the buds open, the insect can be then controlled by
applications of nicotine-sulphate.
[Illustration: FIG. 9.
(1) Peach leaves attacked by Black Peach aphis. (2) Colony of Cabbage
aphis on leaf. (3) Stem of insignis pine attacked by Chermes. (4) Grape
Phylloxera and galls on vine roots. (5) Grape Phylloxera galls on vine
leaf. (6) Woolly aphis on apple twig. (7) Galls of Poplar aphis. (Figs.
1, 2 and 6 by W. C. Davies; Fig. 4. after U.S. Dept. Agric.; Fig. 5.
after N.Z. Dept. Agric.)]
CABBAGE APHIS(_Brevicoryne brassicæ_).--The cabbage aphis, or cabbage
green fly, is widely distributed throughout the world, and has become a
serious pest in New Zealand, causing considerable damage to cruciferous
crops; it infests rape, turnip, cabbage, Brussels sprouts, cauliflower,
as well as related weeds, such as wild mustard, shepherd’s purse and
watercress. Most damage is done during dry seasons, when the plants
succumb more readily to attack; if the insects are numerous, they cause
the leaves to curl, and give a greyish appearance to infested plants,
which may become flaccid and sticky from the copious honey-dew of the
insect. The wingless forms are bluish in colour and coated with a
greyish powder, but the winged females have the head and thorax black
and the abdomen greenish (Fig. 9, 2). In New Zealand all stages may
be found throughout the year on winter crucifers or on weeds, though
reproduction is retarded during the winter; in the spring the winged
females fly to young crops. In very cold climates eggs are laid in the
autumn, and these survive the winter. The cabbage aphis is attacked
by a number of parasites, and usually the brownish empty shells of a
large number that have been destroyed by a small parasite are to be
found at any time; other important enemies are the hover-flies, the
eleven-spotted ladybird beetle, and the Tasmanian aphis-lion. The
insect can be controlled by spraying with nicotine-sulphate to which
soap has been added.
PINE TREE CHERMES(_Chermes pini_).--This is a widely-distributed
species, occurring upon both Austrian and insignis pine in New Zealand.
The insect lives in colonies upon the cones, twigs and branches, as
well as around the bases of the needles; each aphis exudes a woolly
covering, which forms conspicuous white masses when the trees are
heavily infested (Fig. 9, 3). Young trees seem to be the more subject
to infestation, from which they may recover as they grow, but some
damage is caused by the insect by a weakening of the trees, especially
where grown in unsuitable localities. It is frequently noticed that
individual trees in a plantation are heavily infested, while adjacent
trees of the same species are not. The wingless form of the insect,
covered by its mat of white threads, is brownish in colour and
ornamented with numerous dark spots; there are no “honey-tubes” on
the abdomen. The life-cycle of this insect becomes complicated, when
it develops on two types of conifers; in the latter case the primary
host is a species of spruce upon which the insect forms galls, and
the secondary host may be larch, Douglas fir or pine, upon which gall
formation is unusual. So far as is known, only the pine-infesting form
of the aphis occurs in New Zealand.
GRAPE PHYLLOXERA(_Phylloxera vastatrix_).--This destructive aphis,
sometimes called the grape louse, is a native of North America, where
it normally infests grape vines. It was accidentally introduced
into the grape-growing districts of France, where it became very
destructive. It later made its appearance in New Zealand. The insect
infests both the leaves and roots of grape vines, the root-feeding
stages being the most destructive, in consequence of which vines are
now grown on resistant root stocks. The leaf-infesting stages of the
insect cause pocket-like galls to form, which open on the upper surface
of the leaf by a narrow aperture concealed under a tuft of delicate
hairs (Fig. 9, 5). In each gall the aphid matures and deposits several
hundreds of eggs, from which wingless females hatch; these wander to
other leaves, and each insect forms a new gall for itself. Several
generations develop thus, but later many of the offspring migrate
underground and join the root-infesting colonies. The irritation set
up by the latter causes yellow flabby nodules to develop on the roots
(Fig. 9, 4). These nodules, or galls, later decay. The root-feeding
aphides are wingless, and reproduce by means of eggs for several
generations. Although they may go on developing thus for many years,
it usually happens that, toward autumn, some of the insects transform
to winged females, which fly to other vines or are carried thence
by the wind. There each female feeds on the lower leaf surface, and
deposits two kinds of eggs, some larger and some smaller; from the
larger develop wingless females, and from the smaller wingless males,
which are unable to feed. After fertilisation, each of these females
deposits a single egg upon the older bark of the vine; such eggs do not
hatch until the spring, when they give rise to the wingless females
that start the galls on the leaves. Control depends on the use of
phylloxera-resistant stocks, since it is from the root colonies of
the aphis that the foliage is re-infested in the spring. An important
feature is to prevent the scion from sending down roots where the union
of the scion and root stock is close to the soil; if such scion roots
form, they should be cut away and the soil removed from the union.
ROSE APHIS(_Macrosiphum rosæ_).--The rose aphis is perhaps one of
the best-known insects of the garden, mainly owing to its prevalence
upon the young growth of all kinds of roses; it sometimes occurs on
apple, tomato and rhododendrons. In a colony some of the insects are
pink, and others bright green, though in the winged forms the head,
antennæ, thorax, a row of spots on each side of the abdomen, and the
“honey-tubes” are black; in both winged and wingless forms the eyes are
red. In the case of severe infestations, plant growth is retarded and
the leaves and flowers become distorted. Control can be effected by
applications of nicotine-sulphate, kerosene, or soap solution.
APPLE WOOLLY APHIS(_Eriosoma lanigerum_).--Although frequently called
“American Blight,” the apple woolly aphis is probably a native of
Europe. It occurs throughout New Zealand, and was a very serious pest
until controlled by the Aphelinus parasite. The presence of this insect
is made apparent by the characteristic white woolly patches (Fig. 9, 6)
which appear upon the apple trees, due to the woolly material secreted
by the aphid. Another feature is that the part of the tree attacked,
even after the insects have disappeared, is disfigured by gnarled
swellings, due to abnormal thickening of the inner bark. This species
also infests apple tree roots, which become similarly malformed.
However, root infestation has been overcome by using root stocks,
such as Northern Spy, that are immune. The individuals comprising
a colony of woolly aphis are variously coloured, yellow, green and
red predominating; a considerable amount of honey-dew is secreted.
This species has been found to migrate to the foliage of the elm and
mountain ash, but in New Zealand the elm-infesting form has not been
found to occur. The insect becomes active in spring, and rapidly
increases until the autumn. Under favourable climatic conditions,
winged females develop and produce males and females, the latter laying
eggs. The woolly aphis is preyed upon by the nine-spotted ladybird,
but, as this beetle is itself the victim of another insect, its utility
is greatly minimised. The most important check to the aphis is the
Aphelinus parasite (_Aphelinus mali_), the influence of which has been
spectacular under New Zealand conditions.
PLUM APHIS(_Rhophalosiphum nymphææ_).--This insect is sometimes
very common during spring upon the shoots and leaves of plum in New
Zealand; in other countries it has been found to migrate to and infest
the flowers and leaves of water lilies. The insects assume various
shades of green, the winged females having the head, thorax, and
legs blackish; the “honey-tubes” vary in colour, and may be reddish,
blackish or yellowish.
POPLAR GALL APHIS(_Pemphigus pupuli-transversus_).--Upon the leaf
stems of poplar trees in many parts of New Zealand sac-like growths
(Fig. 9, 7), measuring anything from half an inch to one inch in
length, may be found. These are the galls formed by the North American
poplar gall aphis. In each gall are colonies of the aphis surrounded
by a mass of flocculent secretion. The walls of the gall are thick and
tough, with the outer surface wrinkled, while at the end, toward one
side, is a slit-like, or sometimes circular, opening surrounded by a
thickened rim, presenting much the same appearance as the mouth of a
sack gathered together and tied. For the most part, these insects are
wingless females only, but during the summer, and particularly toward
the end of autumn, winged females develop and migrate to cruciferous
plants, such as cabbage, rape, mustard and turnips, or weeds allied to
these cultivated forms, upon the roots of which they establish colonies
surrounded by a woolly secretion. In spring a return migration to the
poplar takes place, and galls are again established.
Leaf-hoppers.
Leaf-hoppers form a group of small, narrow-bodied, sap-sucking insects;
as the name implies, they infest the foliage of a variety of plants,
and when disturbed have the habit of suddenly leaping or hopping to
safety; the species present in New Zealand are usually of a greenish
or yellowish colour. The adult insect is winged (Fig. 8, K, L), and
the female lays her eggs in the plant tissues (H); from these eggs the
young wingless hoppers (I) hatch and attack the plant; as they grow,
wings develop (J), but until then the insect depends for locomotion
upon its hopping powers.
The most outstanding species in New Zealand is the apple leaf-hopper
(_Typhlocyba australis_). This insect causes considerable damage to
apple trees unless controlled, which can be effected by spraying with
nicotine-sulphate against the young insects in the spring.
White-flies.
White-flies, or mealy-wings, are minute sap-sucking insects, having
the body and wings covered with mealy wax. The female (Fig. 8, P) lays
her eggs, frequently in circular batches, upon foliage, and the young
insects (N) are active, but settle down and commence feeding soon after
hatching. Later the insects change to another form (O), without legs
and antennæ, and so resemble scale insects to a certain extent; from
the latter, however, they may be distinguished by the waxy covering,
bearing spine-like processes, and by being surrounded by a distinct
marginal area. An important species in New Zealand is the greenhouse
white-fly (_Trialeurodes vaporariorum_), against which fumigation with
calcium cyanide is the best as a check.
Thrips.
The foliage of many plants is sometimes infested by very minute black
insects, known as thrips. A species commonly met with is that found
upon ripe peaches. Thrips are readily identified by the structure of
the wings (Fig. 8, 4), which are but narrow strips fringed with long,
rigid hairs. These insects, by puncturing the plant tissues and sucking
up the nutrient sap, very often are responsible for infecting healthy
plants with disease, such as mosaic.
According to the species of thrips, the female lays her eggs either
in the plant tissues or upon the surface. The young insects are
wingless, but attack the plant in the same manner as does the adult;
as development proceeds, the insect transforms to a pupa, from which
the adult ultimately emerges. A characteristic symptom of thrips
infestation is a silvering of the foliage, while the leaves are further
rendered unsightly by the minute specks of hardened excreta ejected
by the insects. Many thrips pass their whole development upon the
host plants, while others pass part of their lives underground. One
of the commonest species met with under glass and out of doors is the
greenhouse thrips (_Heliothrips hæmorrhoidalis_). Thrips are readily
controlled by means of nicotine-sulphate.
CHAPTER VII.
Leaf-Feeding Insects.
Leaf-feeding insects have their mouth-parts developed for the biting
off and mastication of their food; such insects are, in general,
earwigs, crickets and grasshoppers, the caterpillars of moths and
butterflies, beetles and their grubs, and the grubs of saw-flies. Such
insects vary, not only in their period of activity, some feeding at
night, others during the day, but also in the manner under which they
set about it. Many feed exposed upon the surface of the plant, while
others require protection, such as is afforded by the webbing together
of leaves. Some feed upon the leaf epidermis only; some eat holes in
the leaf-surface, or gnaw irregular notches from the leaf-edge; while
the grosser feeders completely devour the whole.
Earwigs.
In many parts of New Zealand the European earwig (_Forficula
auricularia_) causes considerable damage in gardens, while in Central
Otago it sometimes ruins the stone fruits. During the winter this
insect lies underground, where the female will be found with her
cluster of eggs. In the spring these eggs hatch, and the small whitish
young earwigs (Fig. 4, 2) emerge from the ground to feed largely upon
the pollen and pistils of flowers. At that time the insects and the
injury they do are not very noticeable, but as the earwigs grow in size
they become conspicuous and extend their depredations to the foliage of
plants and to fruit. Earwigs are nocturnal in their habits, and during
the day take shelter among fallen leaves, under stones, sacking, or
boards, etc., lying on the ground, and may even burrow into the soil
itself.
In the control of the earwig, a great deal can be done by what may be
called clean gardening--that is, the removal of all places likely to
shelter the insect above ground during the day. Another important means
is systematic trapping, one of the simplest methods being to place
crumpled newspapers on the ground at nightfall, in which many of the
insects will seek shelter, the papers being collected and burned next
day. But the best method is the use of the following poison bait:--With
12lb. of bran mix 6 quarts of water, to which has been added 5oz.
of glycerine and 6oz. of sodium fluoride; to this mash add 4lb. of
treacle, taking care to thoroughly mix the whole.
This bait is spread at nightfall in places frequented by earwigs,
and should be repeated regularly, especially after wet weather. It
is obvious, if satisfactory results are to be secured, that there
should be a co-operative campaign organised among the residents of an
earwig-infected district.
Crickets and Grasshoppers.
Fortunately, neither crickets nor grasshoppers (Fig. 10, 1 and 2)
are a serious menace to the New Zealand horticulturist, though at
times, especially in the warmer parts of the country, crickets may
do some extensive damage. The control of these pests is a difficult
matter, since they are mobile insects, and breed in places outside
the boundaries of the horticulturist’s activities. Some benefits can
be secured, however, by thorough cultivation, which breaks up the
egg-masses which are placed in the ground. In the case of serious
outbreaks, the use of a poisoned bait would have to be resorted to, and
the following is recommended from the several recipes in use:--With
25lb. of bran mix 3 or 4 gallons of water in order to make a thin mash;
to this, add 2 quarts of molasses and 1lb. of Paris green, thoroughly
mixing the whole. If crickets alone are to be dealt with, then use
a little more of the Paris green. This mash is spread on the ground
invaded by the insects.
Caterpillars.
Of the leaf-feeding insects, the caterpillars of moths are the most
commonly met with, there being a considerable number of destructive
species. Caterpillars (Fig. 10, 3) can be readily distinguished by
their structure from the grubs of other insects. They resemble short
earthworms in shape, and in having the body divided into several
segments, of which there are usually thirteen; but here the resemblance
to worms stops. There is a distinct head--the first segment--provided
with jaws, and on the under side of each of the next three segments,
or thorax, is a pair of short feet. The remaining segments comprise
the abdomen, and possess sucker-like feet, varying in number according
to the kind of caterpillar; in some forms there may be as many as five
pairs of such feet, in some three pairs, and in others two, but in all
the pair on the terminal segment persists. Many caterpillars are more
or less hairy, and others comparatively nude. The following are amongst
the most injurious kinds:--
LEAF ROLLERS.--It is a common sight to see small greenish caterpillars
sheltering between two or more leaves of plants that have been
tied together by the silken threads spun by the caterpillars;
protected thus, the insects feed more or less in security. These
caterpillars belong to several species of the tortricid moths,
which are themselves comparatively small and drab in colour. Of
these species, the most abundant one, comprising over 84 per cent.
of the leaf-roller population, is the Australian apple-leaf roller
(_Tortrix postvittana_); the caterpillars of this insect by no means
confine their attacks to the apple, but feed equally well upon pear,
orange, grape, rose, insignis pine, oak, pelargoniums, etc. Apart
from attacking the foliage, the caterpillars frequently tie a leaf to
the surface of apple and stone fruits, and feed upon the skin of the
latter, causing a blemish.
The apple-leaf roller passes the winter in the caterpillar stage
between two leaves. In the spring these caterpillars transform to
pupæ, which give rise to moths from the end of August to about the
end of October; there are at least two broods of caterpillars during
the year, but the limits of these broods are not clearly defined. The
caterpillars are attacked by several species of parasites.
Leaf-rollers are easily controlled by the arsenical sprays used against
codlin moth, but these sprays must be continued into the late summer
after their need against codlin moth is past.
DIAMOND-BACKED MOTH(_Plutella maculipennis_).--The caterpillars of this
moth (Fig. 10, 4) are commonly found attacking the leaves of cabbages,
rape and other cruciferous crops and weeds. These caterpillars are
small and greenish, and, if disturbed, suddenly drop suspended by
a silken thread attached to the plant. The damage they do is very
often extensive, considerable areas of the foliage being devoured.
When fully developed, each caterpillar spins a silken cocoon on the
under side of the leaf, and there transforms to the pupæ, from which
a moth eventually emerges. The insect is small, narrow, and has a
light-coloured, diamond-shaped marking along the back. The moth is
nocturnal, and shelters amongst the denser foliage during the day; it
emerges at night, and lays its eggs upon the leaves. The life-cycle
from eggs to adult occupies some 36 days, more or less, according to
the season, and there may be six or seven generations during the year.
In control, an important point to note is that the diamond-backed
moth breeds upon cruciferous weeds--watercress, shepherd’s purse, and
hedge-mustard--as well as on the old plants of a crop left in the
ground; it is from such places that infestation of future crops arises,
and the clearing up of such breeding places should be given close
attention. Under garden conditions, control can be secured by spraying
the plants with arsenate of lead (to which a spreader must be added in
the case of cabbage), which should be done especially when the plants
are young.
KOWHAI MOTH(_Mecyna maorialis_).--The caterpillar of this native moth
sometimes becomes epidemic, when it does considerable damage to kowhai,
broom, lupins, and sometimes clover. The caterpillar, which measures
about an inch when mature, is of a greenish colour, having rows of
black tubercles with white centres along the sides, and a double
row of white spots along the back; from the black tubercles black
bristle-like hairs arise. The caterpillar spins a silken cocoon, in
which it pupates. The moth is comparatively small, the fore wings being
yellowish-brown with darker markings, and the hind wings orange-yellow
with a blackish border. There are at least two broods of caterpillars
annually: the first in the spring, and the second during autumn.
Arsenate of lead will give effective control on garden legumes.
CUT-WORMS.--This term is applied to the caterpillars of a number of
night-flying noctuid moths; these caterpillars are smooth-bodied and
rather worm-like, in some cases measuring from one and a-half to two
inches in length when full grown. They feed at night, and their method
of attack is characteristic in that they nip off young plants close
to the ground (Fig. 10, 5), so that the latter fall over, when they
are devoured by the caterpillars; this habit has given rise to the
name “cut-worms.” During the day the cut-worms are to be found curled
up in the ground close to the plants they have been attacking. The
moths of these caterpillars are rather stout-bodied, and measure about
three-quarters of an inch long. One of the commonest species is the
cosmopolitan greasy-cut-worm (_Agrotis ypsilon_).
[Illustration: FIG. 10.
(1) Cricket. (2) Grasshopper. (3) Caterpillar. (4) Diamond-backed
Moth--a, adult moth; b, egg; c, larva; d, pupa. (5) Cut-worm lying by
damaged plant. (6) Tomato-worm Caterpillar--a, adult; b, larva. (7)
Cabbage White Butterfly--a, adult; b, egg; c, larva; d, pupa. (8) Larva
case of Bag-moth.]
Though cut-worms are active throughout the growing period of plants,
most damage is done to young and tender plants at the time of
establishment, and this is particularly noticeable in the spring. When
plants are grown isolated in rows, and the area is not too large,
complete protection from cut-worms can be secured by enclosing each
plant in a tin collar pushed into the ground and projecting a few
inches from the surface; these collars are removed when the plant is
well established. In localities where cut-worms are very troublesome it
is advisable to reduce their numbers by means of a poison bait made as
follows:--50lb. of bran and 1lb. of Paris green are thoroughly mixed in
a dry state; when this is done, and just before being used, the bran is
moistened with water, sweetened with molasses, until the bait reaches a
crumbly, but not saturated, condition. This bait may be broadcast over
the infected area or laid around each plant as a barrier. This bait
must be applied every few days until the plants have reached a stage
when they are able to withstand cut-worm attack.
A great deal can be done to check cut-worms by removing dense growths
of weeds and rough herbage growing in unused parts of the garden; in
such places the insects breed, and are a source of infestation. Another
point to consider is that thorough cultivation will destroy many pupæ
that are lying underground, and which would otherwise give rise to
another generation of moths.
“ARMY-WORMS.”--These caterpillars are similar in their appearance
and general habits to the cut-worms, but differ in their method of
attack. When present in numbers, they move through a crop--especially
cereals--eating as they go, and leaving nothing but devastation in
their wake, much as does an invading army on the march. They are not of
so much interest to the horticulturist as to the farmer.
TOMATO-WORM(_Heliothis armigera_).--This caterpillar (Fig. 10, 6) is
one of the most conspicuous caterpillars met with in the garden. Its
habit of boring into and eating the contents of tomatoes gives it the
name of “tomato-worm.” It is a cosmopolitan insect, and is especially
destructive to flower buds and fruit, a wide range of plants being
attacked. The caterpillars vary in colour, some being greenish and
others brownish, with reddish, yellowish or white markings. The moth,
which belongs to the noctuid group, is on the wing both day and night,
mostly during the earlier part of the year; it is a stoutly-built
insect, measuring somewhat over half-an-inch long; its colour is
a brownish-orange, with oblique darker bands on the wings. As the
insect passes the winter and spring as a pupa in the ground, thorough
cultivation will help to destroy a considerable number. The use of
arsenate of lead sprays, however, is the most effective control for the
caterpillars.
HAWK OR SPHINX MOTH(_Sphinx convolvuli_).--This conspicuous insect
and its caterpillars are most abundant in the Auckland province,
though found as far south as Christchurch. The caterpillars feed on
convolvulus, but do considerable damage to the foliage of the kumara
and sometimes tobacco. The caterpillar is the largest met with in the
garden; it is stout in form, and measures up to 3-1/2 inches when fully
grown. It is to be recognised at once on account of the dark red,
horn-like process arising from the end of the body. The caterpillar
may be of two colours--the one green, with diagonal yellow bars on the
sides; the other, brownish-yellow, with dark lines on the back and
sides. From about February to November the insect lies in the ground as
a pupa. The latter can be recognised by a curved process arising from
the head and lying along the body. The moth flies rapidly during the
last and earlier months of the year; it is a large, conspicuous insect,
about 1-1/2 inches long, with greyish-brown mottled wings, while the
abdomen is conspicuously barred with white, red and brown. Arsenate of
lead against the young caterpillars during November to February would
act as an efficient control.
CABBAGE WHITE BUTTERFLY(_Pieris rapæ_).--This butterfly (Fig. 10, 7)
is a recent importation, having been first noted at Napier in 1930.
Since then it has spread with marvellous rapidity throughout the North
Island, and has appeared in the South Island, in the vicinity of Timaru.
The caterpillars of this insect are particularly severe in their
attacks upon the foliage of cabbages and cauliflowers, though they
also feed upon many other related plants, such as lettuce and radish,
besides cruciferous weeds. The caterpillars of the white butterfly
are not to be confused with those of the diamond-backed moth, already
described. The full-grown white butterfly caterpillar is a conspicuous
insect, and measures up to an inch and a-quarter in length; it
is easily distinguished by its leaf-green colour and velvet-like
appearance, while down the centre of the back is a narrow orange
stripe, and on each side a brownish line formed of little spots. The
chrysalis measures about three-quarters of an inch long, having a
pointed process from the head, and a keel-like ridge on its back,
while the colour varies according to the surroundings with which the
chrysalis blends; it is not protected by a cocoon of silk, and may be
found upon the food plant or any other support near by.
The butterfly itself is a very conspicuous insect, measuring about two
inches across the expanded wings. The female is of a yellowish-white
colour, with darker to blackish markings at the fore-angles of the
front wings, while there are two similar spots on the surface of the
same wings, and one on the hind pair. The male is whitish, with a dull
greyish-green or bluish hue, marked much as the female, except that
there is only a single spot on the surface of each wing.
The eggs (Fig. 10, 7b) are bottle-shaped, and stand erect upon the
leaf surface, where they are laid singly, and not in batches; they are
visible to the naked eye. The eggs hatch within a week after being
laid. There are several generations each year.
The cabbage butterfly can be controlled by the use of lead arsenate. It
has been found effective when planting out to first dip the seedlings
in lead arsenate at the rate of 1lb. in 50 gallons of water, to which
1lb. of laundry soap is added as a spreader. During the growth of the
crop the same strength of arsenate and soap can be applied as a spray.
MAGPIE MOTH(_Nyctemera annulata_).--One of the commonest and most
conspicuous day-flying insects of the garden and field is the magpie
moth. It is black in colour, relieved by an orange-banded abdomen and
whitish spots on the wings, two on each of the front wings and one on
each hind one. Its black, hairy caterpillars, commonly called “woolly
bears,” have narrow brick-red lines along the body, and very often do
some considerable damage to cinerarias; they also attack weeds, such as
ragwort and groundsel.
The small globular eggs are laid in clusters on the leaves of the food
plant. At first they are pale green, later becoming dark yellow, and
just before the young caterpillars emerge from them they change to a
leaden colour. When fully fed, the caterpillar seeks a sheltered place
(beneath stones, under, bark, etc.), and there spins a loose cocoon, in
which it transforms to the chrysalis; the latter becomes blackish or
brownish in colour, with yellow markings. There are several generations
during the year.
Cinerarias can be protected by spraying with lead arsenate, or, better,
by removing the caterpillars by hand and destroying them.
CABBAGE TREE MOTH(_Venusia verriculata_).--The foliage of the
cabbage tree is frequently holed on the surface and notched along
the edges--this is the work of the cabbage tree moth caterpillars.
The history of the insect is as follows:--The nocturnal moth
measures about an inch and a-half across the expanded wings, which
are characteristically coloured by alternating chocolate-brown and
yellowish-white lines running from wing-tip to wing-tip across the
body, so that the insect merges into the general pattern and colour
of a dead leaf, upon which it usually rests. The eggs are green, and
at first blend with the green leaf, on which they are often laid in
batches; when on dead leaves they become conspicuous. Later the eggs
change colour to brown, and finally red. The caterpillars congregate in
the unopened foliage, and their injury becomes apparent as the leaves
open. The larvæ transform to chrysalids in silken cocoons, loosely
spun in any suitable crevice upon the trees. If it was necessary and
practicable to protect ornamental cabbage trees from the attacks of
this insect, it could be done by removing dead leaves from the crown
and spraying with arsenate of lead to which laundry soap had been added.
BAG MOTH(_Œceticus omnivorus_).--This is an insect that never fails to
attract attention on account of its cigar-shaped bags (Fig. 10, 8),
constructed by the larvæ, and are to be found attached to a variety of
plants, upon the foliage of which the larvæ feed, though they are not
serious pests. Each caterpillar spins its own tough silken bag, which
it never leaves, and to the outside of which it frequently attaches
fragments of leaves and twigs. Though the male is a normal moth,
and flies about (it is practically black, and densely haired, with
translucent smoky-black wings having an expanse of about an inch and
a-quarter), the female develops in an abnormal manner, and assumes a
grub-like form, never leaving the bag woven by its caterpillar.
If it should be found necessary, as sometimes happens, the only
satisfactory way of controlling the bag-moth is to remove by hand and
destroy.
Beetles.
Unlike the caterpillars of moths, there are very few beetles in New
Zealand that are important leaf-feeders. Though few in numbers,
however, the outstanding ones are very destructive. The beetles
themselves, as well as their larvæ, according to the species, may
attack foliage, but in other cases it is only the beetles that feed
on foliage while their larvæ live underground on roots. The following
species are outstanding:--
COCKCHAFERS.--These are the adults of the grass grubs, and there are
several species, all native to New Zealand. The commonest and most
destructive one (Fig. 11, 1a) is the so-called brown beetle (_Odontria
zealandica_), misnamed the “turnip fly,” which is on the wing for about
six weeks each year, during November and early December as a rule. It
swarms at dusk, creating a loud, droning sound, and is responsible for
widespread damage by defoliating garden plants and field crops, as well
as trees.
[Illustration: FIG. 11.
(1) a, Brown-chafer beetle; b, antenna of beetle, showing finger-like
processes; c, larva or grass grub. (2) Bronze beetle. (3) a, Gum-tree
weevil; b, egg capsule; c, larva. (4) Eucalyptus tortoise beetle. (5)
a, Pear saw-fly; b, larva from the side; c, larva from above. (6) Pear
midge.]
This beetle is easily identified. It is rather plump-bodied, brownish,
smooth, and measures about three-eighths of an inch long. Like all
beetles, the front wings are hard, and form a cover over the body when
closed; these hardened wings, or elytra, do not reach quite to the end
of the abdomen, the tip of which remains uncovered. Another definite
character is found in the antennæ, which terminate in finger-like
processes (Fig. 11, 1b). There are several species of cockchafers, to
which all these characteristics, except the colour, might be referred,
but none is so abundant as the species under review. There is one,
however, that is on the wing about the same time as, or a little
earlier than, the brown beetle. This species is somewhat larger, about
half an inch long; it is sparsely clothed with hair, and the elytra are
marked by broad brown stripes, alternated with very narrow darker ones.
The brown beetle lays its spherical eggs in the ground, preferably
amongst the roots of grass, strawberries, etc. The grubs (Fig. 11, 1c)
are well known as grass grubs; they are whitish in colour, the swollen
terminal segment of the abdomen being very often darker. These grubs
are sometimes called “curl-grubs,” from their habit of lying doubled-up
when at rest or feeding in the ground. Towards September each year
the grubs of the brown beetle pupate prior to the beetles emerging
in November. These grubs will be referred to later under the chapter
dealing with subterranean insects.
In gardens and nurseries, the depredations of the beetles may be
lessened by spraying with lead arsenate, or by the use of sulphur
smudges. The use of smudges was developed very effectively as follows
by Mr. D. J. Buchanan, forest ranger at the Tapanui State Forest
nurseries. Sulphur is spread on strips of scrim, which are then rolled
up and placed in containers, such as old paint pots. The latter are set
about the nursery, and fired at evening, when they will burn throughout
the night, the fumes acting as a deterrent to the beetles. When only a
few plants are to be protected, such as bush roses, the beetles can be
warded off by allowing a hose to play over the plants throughout the
night.
Another common cockchafer which is on the wing most of the summer and
autumn is the green manuka beetle (_Pyronota festiva_). This insect is
capable of causing considerable damage as a defoliator. It is active
both day and night. The general colour is bright green, with a dark
stripe down the middle of the back, though some specimens are brown or
coppery; the legs are orange-yellow, and the length of the insect is a
little over a quarter of an inch.
BRONZE BEETLE(_Eucolaspis brunneus_).--This insect (Fig. 11, 2) is very
often confused with the brown beetle, from which, however, it is easily
distinguished. It is active during the day, and attacks the foliage and
fruit of a great variety of plants, eating holes from leaves, so that
the latter appear as if they had been subjected to a charge of shot,
or devouring the epidermis from fruits and berries. This beetle is
active during November to January; it measures about one-sixteenth of
an inch long, is oval in outline, and varies in colour from yellowish,
with darker markings, to greenish or bronzy-black; the antennæ are
comparatively long, and do not terminate in any unusual manner, as do
those of the cockchafers. A characteristic habit of the bronze beetle
is to leap off the plant if disturbed; this habit has been responsible
for the group to which this insect belongs being called “flea beetles.”
The bronze beetle lays its eggs in the ground, where the larvæ feed,
though they are not injurious in that stage. The beetles are to be
controlled by the use of lead arsenate.
GUM TREE WEEVIL(_Gonipterus scutellatus_).--Both the adults and larvæ
of this Australian weevil attack eucalyptus foliage, particularly
bluegum, in most parts of New Zealand, the adult weevils eating from
the leaf margin, as well as devouring tender shoots, while the larvæ
cut elongated holes from the leaf surface.
The weevil (Fig. 11, 3a), which is of a tawny to brownish-black colour,
and clothed with yellowish-white and golden hairs, measures from a
quarter to one-third of an inch in length; it possesses a short snout
on the head. The eggs are yellowish, and are packed in a hard, black
capsule (Fig. 11, 3b), attached mainly to the surface of young leaves.
The larvæ (Fig. 11, 3c) are legless, like those of all weevils, and
yellowish at first, when they are studded with small black dots, and
have a dark stripe along each side. Frequently these young larvæ are
seen with a tail-like thread of blackish excrement projecting from the
posterior end. The plump, fully-developed grub is yellowish-green, with
a wrinkled skin, and is slug-like in general appearance. Pupation takes
place in the ground. This insect over-winters in the adult stage, and
large numbers of the weevils are very often to be found beneath loose
bark on the tree trunks during the winter. Control depends upon the use
of an egg parasite which has been established in certain localities of
the Dominion. In the case of small ornamental trees, spraying with lead
arsenate to which laundry soap has been added should be effective.
EUCALYPTUS TORTOISE BEETLE(_Paropsis dilatata_).--This is another
Australian insect restricted so far to the East Coast districts of the
South Island, where it attacks eucalyptus foliage in company with the
weevil. The beetle (Fig. 11, 4) is tortoise-shaped, varies in colour
from reddish-yellow to reddish-brown, with darker markings on the
back, which is pitted by minute depressions, and has a length of from
one-third to half an inch. Like the weevil, this beetle passes the
winter beneath loose bark.
The eggs are conspicuous and cigar-shaped, being laid in clusters,
lying more or less on their sides, upon the foliage. The larva is
rather plump, and pointed posteriorly; it possesses legs, while at the
tip of the body is a sucker-like false foot. The general colour is
yellowish, varying to a rosy-pink, there being a darker stripe down the
back, while along each side is a similar one above a row of black dots.
PEAR AND CHERRY SLUG, OR SAW-FLY(_Caliroa limacina_).--The slug-like
larvæ of this insect are very abundant upon hawthorn foliage, and if
not controlled do considerable damage to cherry, plum, pear, and peach.
These larvæ (Fig. 11, 5b) are very often called leeches, and devour
the epidermis, exposing the skeleton of the infested leaves; they are
slimy, of a dark green, though orange-coloured immediately after a
moult, and the head end is much enlarged, giving a clubbed shape to the
body, along the under side of which are several false legs. Pupation
takes place in the ground. The adult (Fig. 11, 5a) measures about a
quarter of an inch long, is rather thickly set, black in colour, and
possesses four transparent wings. The female deposits her eggs in the
tissue of the foliage by means of a saw-like ovipositor--hence the
name “saw-fly”--which is thrust through the lower epidermis of the
leaf, when a pocket is formed to receive the egg; each egg pocket
forms a little pimple on the upper surface. This insect is very
easily controlled by spraying foliage infested by the larvæ with lead
arsenate.
Another saw-fly closely related to the foregoing species is the willow
saw-fly (_Pontania proxima_). This species has only recently appeared
in New Zealand, and its larvæ live in galls, or swellings, on the
foliage of willows.
PEAR MIDGE(_Perrisia pyri_).--A serious pest of pear trees, which for
some years retarded the culture of pears, especially in the Auckland
district, is the pear midge. This is a minute, delicate, two-winged
fly (Fig. 11, 6), measuring about one-twenty-fifth of an inch long;
it has a blackish head and thorax, and an orange-red to brownish
abdomen. The female alights upon young leaves just burst from the
bud; and, while they are yet curled, lays her eggs between the folds.
The larvæ, on hatching, live protected in the curled leaves, which
they attack, and which never unfold. The result is that the infested
leaves eventually turn black and brittle, and cease to function. The
fully-developed larvæ drop to the ground, which they enter, and there
pupate. The midges become abundant in early spring, when the first
young pear foliage develops, and they keep on producing generation
after generation until the autumn. The winter is passed in the larval
stage underground beneath the trees.
A parasite has been established against the pest, and is doing good
work. The insect can be reduced to a large extent by thorough winter
cultivation, especially beneath the trees. The insect’s larvæ, being
protected within the curled-up leaves, are not reached by ordinary
sprays, but Dr. R. H. Makgill, of Henderson, secured some excellent
results on young trees by the use of nicotine.
OLEARIA GALL MIDGE(_Cecidomyia oleariæ_).--In many parts of New
Zealand where _Olearia forsteri_ is grown as a hedge, it is very often
disfigured by the formation of malformations, or galls. These are
caused by a native midge known as the olearia gall midge. The midge
itself resembles the pear midge in structure, but is larger, measuring
from one-tenth to one-eighth of an inch long; it is conspicuous on
account of its black thorax and blood-red abdomen. In early spring the
midges appear and lay their conspicuous masses of bright red eggs upon
the buds of the developing shoots. The larvæ, on hatching, set up an
irritation in the rapidly-developing tissues, causing the latter to
swell and become malformed into bunches of rosette-like galls. If the
latter are cut open, a number of the yellowish larvæ will be found,
each in its own compartment within the fleshy gall. There is only one
brood of adults each year. Control can be effected to a great extent by
cutting back and burning the badly-infested parts during winter, and by
pruning the young growth carrying the eggs in the spring. Spraying with
nicotine when the midges are active should also help to protect the
plants.
CHAPTER VIII.
Boring and Underground Insects.
CODLIN MOTH(_Cydia pomonella_).--The codlin moth caterpillar burrows
in developing apples and pears, and such “wormy” fruit is known to
everybody.
The moth itself is seldom seen, since it lies concealed until after
nightfall, when it becomes active and lays its eggs. The insect
(Fig. 12a) measures about three-quarters of an inch long, and is
inconspicuously, though beautifully, coloured; the fore wings, which
cover the body when closed, are light grey, crossed by fine bands of
a darker hue, giving the appearance of watered-silk, while at the
extremity of each wing is a large bronze spot; the hind wings, seen
only when expanded, are of a light brown colour. The minute flat eggs
are laid on the foliage of leaves, on the fruit, or even on young bark;
they appear at first as glistening white specks, but, as development
advances, a red ring develops, and finally a black spot just prior to
the caterpillars hatching.
In some places the first larvæ developing in the spring enter the fruit
by way of the calyx, but under New Zealand conditions it is more usual
for entry to be made by boring through the skin of the apple. Having
completed their development in the fruit, the caterpillars bore their
way out and spin their cocoons beneath the loose bark of the tree
trunks; in these cocoons pupation takes place, and from them the next
generation of moths develops.
Although in New Zealand there is usually only one generation produced
each year, three or even four develop in other countries. The winter
is passed by the larvæ in their cocoons, and pupation takes place just
prior to the period when the moths emerge in the spring. As the moths
continue to emerge and lay their eggs for a period extending from
November to February, it is essential that regular applications of
arsenate of lead be made during that time in order to protect the fruit
from the larvæ hatching from the eggs laid by the moths. In localities
where the spring larvæ enter the calyx of the fruit, it is essential to
apply the first spray just after the petals fall, so that the poison
may lodge in the calyx before it closes. The removal of rough bark from
the trunks of both apple and pear trees is a help in controlling the
insect. Another method sometimes used is to band the tree trunks with
strips of scrim; under these bands the larvæ collect, and the former
can be later removed and destroyed with their tenants.
CURRANT CLEAR-WING BORER(_Sesia tipuliformis_).--This destructive
moth has been carried to and established in New Zealand, as well as
many other parts of the world. In currant gardens its larvæ cause
the death of canes by eating out the pith. The moth (Fig. 12b) is a
very conspicuous and beautiful insect; the wings, which expand to
about three-quarters of an inch, are transparent and bordered with
golden-purple, a bar of the same colour crossing the surface of the
fore wings; the body (about half an inch long) is metallic-purple, the
thorax having a yellow stripe on each side, while the abdomen, barred
with golden bands, terminates in a fan-shaped tuft of purplish hairs.
The moths are active each year in the spring, when they lay their
brownish, globular eggs singly on the bark of the currant canes. The
resultant larvæ bore into the stem and destroy the pith, passing the
winter in the damaged canes. In the following spring the larvæ become
active once more and approach the surface, where pupation takes place
shortly before the moths emerge.
There is only one generation each year, and control lies in the removal
and burning of infested canes in late winter.
TOMATO STEM BORER(_Gnorimoschema plæsiosema_).--Tomato growers are
frequently faced with the problem of the destruction of tomato plants
caused by the attacks of the larvæ of the tomato stem borer moth. This
insect caused considerable damage for the first time in Auckland some
fourteen years ago, though it was known in other parts of the country
as well.
The moth itself (Fig. 12c) is a small one, measuring about a quarter
of an inch with the wings closed. In this position the insect is
wedge-shaped and conspicuous. Against the general greyish-brown colour
is a dark brownish area on each side. The eggs are laid on the tomato
leaves, in which the young caterpillars tunnel as they work toward
the leaf petioles, down which they burrow into the main stems. In the
damaged stems, pupation takes place. Under favourable conditions, this
insect may pass through at least three generations during the season.
Control depends upon sanitation and the use of arsenate of lead
sprays. All infested stems, together with plants after the crop has
been removed, should be burned; as the insect is known to attack
potato plants and tubers, care should be taken to destroy all potato
tops after harvesting. Frequent applications of arsenate of lead are
essential to protect the tomato plants, especially during the earlier
part of the season.
When on this subject, mention should be made of the potato-tuber
moth (_Phthorimæa operculella_), which is somewhat similar to the
tomato-stem borer, both in appearance and habits. The larva of this
insect is best known from its habit of boring through potato-tubers;
these burrows become filled by a fungus after the larvæ have vacated
them. The adult potato-tuber moth is a night-flyer, and lays its eggs
upon the leaves of the plants; the larvæ burrow down the stems, and may
even reach the tuber below ground. When seed is not properly buried,
the moth will also lay its eggs in the “eyes,” and so directly infest
the tuber; this danger applies also to potatoes in store or in bags.
In the control of the potato-tuber moth, the following points should
be noted:--Select only sound seed and cover well when planted. On
harvesting the crop, do not leave the bagged potatoes standing in the
field overnight, as they are exposed to infestation; neither cover
the open bags with the potato-tops, as is commonly done, since this
will attract the moths. Destroy all tops immediately after harvesting.
Dusting potatoes in store with slaked lime will tend to act as a
protection against the moth.
[Illustration: FIGURE 12.
A--1, Codlin moth; 2, codlin larva in apple. B--1, Currant clear-wing
moth; 2, clear-wing moth larva in stem. C--1, Tomato stem-borer moth;
2, larva of moth; 3, damaged tomato stem. D--1, A long-horn beetle; 2,
larva of long-horn beetle. E--1, A leaf-mining fly; 2, leaf attacked by
leaf-miner. F--1, Subterranean grass-caterpillar moth; 2, subterranean
grass-caterpillar. G--1, A click beetle; 2, a wire-worm. H--1,
Larger narcissus fly; 2, smaller narcissus fly. K--1, A subterranean
spring-tail; 2, a leaf-eating spring-tail.]
ROUND-HEADED BORERS.--Apple, almond, and citrus trees, together
with gooseberry and such ornamental and shelter trees as poplars,
tree-lucerne, and goat-willow, are sometimes damaged by round-headed
borers, which tunnel in the stems and branches. These borers (Fig. 12d)
are white in colour, narrow-bodied, and cylindrical, the segments
being usually well defined, and belong to a group of beetles known
as long-horned beetles, a group of insects to which the common hu-hu
beetle belongs. These beetles are narrow-bodied, and their antennæ are
comparatively long and conspicuous.
To control these pests, the only thing to do is to cut out and burn
the badly-infested parts. Where a borer is located (and this can be
frequently done by the presence of the powdered wood ejected from the
burrows), the culprit may be killed by injecting into the tunnel some
carbon bisulphide and plugging up the openings with some clay or other
similar substance.
LEAF-MINING FLIES.--Very often the leaves of cineraria and
chrysanthemum are disfigured by the tortuous tunnellings of the maggots
of minute flies (Fig. 12e). The adult insects are two-winged, and in
structure resemble in many respects miniature houseflies. The eggs
are laid in the leaf tissues, in which the whole development of the
maggots and pupæ takes place. The white maggots are small, legless and
headless. Spraying with black-leaf 40 would act as a deterrent to the
flies, while infested leaves should be removed and destroyed before
infestation becomes general.
GRASS GRUB(_Odontria zealandica_).--As explained in the preceding
chapter, the grass grub is the larva of a native cockchafer beetle
(Fig. 11, 1). This grub, by feeding upon roots, causes extensive damage
to pastures and lawns, as well as to many garden plants, including
strawberries. In the case of pasture and lawns, the presence of even a
considerable number of grass grubs is not detrimental unless they occur
concentrated in definite areas, when the damage is pronounced. With
garden plants, however, which are isolated when compared with the dense
root masses of grasses, the attacks of one or two grubs upon the roots
of a single plant may cause serious injury.
Grass grub damage to grasses is not merely due to attack upon
the roots. While feeding, the grubs swallow soil with the roots,
rendering the former spongy, and so disturb the normal circulation
of moisture about the grass roots. In the case of infested lawns,
it is advantageous to roll infested areas in order to pack the soil
pulverised by the grubs, and re-establish normal circulation of soil
moisture. Another important feature in grub control is to stimulate
root development by means of fertilisers. A recently-developed method
of “grub-proofing” lawns is to broadcast over every thousand square
feet of turf to be treated one bushel of screened sand or clean soil,
in which 5lb. of lead arsenate powder have been intimately mixed. This
is said to remain effective for a period of three years; but such
fertilisers as nitrate of soda, superphosphate, sulphate of potash,
and potassium chloride should not be used on “grub-proofed” turf, as
they react with the lead arsenate, and reduce its effectiveness, though
rotted manure or ammonia sulphate may be used.
The control of grass grubs damaging the roots of strawberry and other
plants is a difficult matter, though some benefit is to be derived
by making holes about four inches deep with a stick in the soil near
to the infested plants and pouring in a little carbon bisulphide; the
holes should be closed immediately. To protect strawberry beds, if
they are not too extensive, the most satisfactory method is to cover
the plants with scrim, stretched on frames, at dusk during November
and early December, when the beetles are flying; this will prevent the
insects from infesting the ground with their eggs. The use of sulphur
smudges, already referred to, is of great importance in this respect.
SUBTERRANEAN GRASS CATERPILLARS.--These caterpillars are the larvæ of
native moths (Fig. 12, f1) belonging to the genus _Porina_, and when
they become epidemic they cause much more extensive damage to pasture
and lawns than do the grass grubs. When full grown, the greyish-black
caterpillars (Fig. 12, f2) reach a length of about three inches; they
are soft-bodied and rather flaccid, and live in underground burrows
of varying depth. After dark, these caterpillars come to the surface
and devour the grass, eating it close to the ground, much soil being
swallowed by the larvæ during the feeding. This soil is evacuated,
and resembles earthworm castings, but is mixed with silk spun by the
caterpillars; the emergence holes of the caterpillars, about the
diameter of a lead pencil, are conspicuous on the surface denuded of
its covering of grass. Pupation takes place underground, and when the
moths emerge the pupæ first move to and project beyond the surface
of the ground; these pupæ are large and easily recognised by the
wing-cases, which are very short compared with the length of the body.
The moths are on the wing during spring and summer, the rest of the
year being spent in the larval stage. The moths are night-flyers, and
are amongst the largest species in New Zealand, their wings having
an expanse of from one to over two inches; they are heavy-bodied
insects, and vary considerably in colour. One of the commonest, species
is brownish-yellow, or sometimes a smoky-grey, with a white streak
bordered with black on the fore wings; the hind wings may be pinkish.
The most satisfactory method of controlling the insect is to roll
infested lawns after dark, in order to crush the caterpillars whilst
feeding on the surface. Flooding an infested lawn with water will bring
most of the caterpillars to the surface, when they can be collected and
destroyed. Spraying grass in spring and early summer with arsenate of
lead will tend to poison the immature caterpillars. There are at least
three species of insect parasites that attack these larvæ, and there
is also a fungus which invades and destroys the whole body, taking the
shape of the insect; such fungus-infested caterpillars are commonly
called “vegetable caterpillars.”
WIREWORMS.--The roots of garden plants and germinating seeds are
often damaged by hard, wiry beetle grubs, reddish-brown or whitish in
colour, called “wireworms,” so named from their resemblance to short
pieces of wire; they have three pairs of legs behind the head and a
sucker-like appendage on the last body-segment (Fig. 12, g2). These
grubs transform to narrow-bodied, brownish or blackish beetles, known
as “click-beetles” (Fig. 12, g1) from their habit, when overturned, of
righting themselves by a springing action, during which a distinct and
sharp clicking sound is made; the spring apparatus consists of a spine,
the tip of which fits into a notch on the under side of the thorax.
Practically nothing is known as yet in regard to the biology of the New
Zealand click-beetles. They are extremely difficult to control, and the
larval stage covers a period of two or more years.
NARCISSUS FLIES.--There are two species of narcissus flies--the larger
(_Merodon equestris_) and the smaller (_Eumerus strigatus_) both occur
in New Zealand. The larvæ of these flies attack bulbs of various
kinds, the hosts of the larger fly being narcissus, hyacinth, tulip,
amaryllis, habranthus, vallota, galtonia, scylla, and leucojum; and of
the smaller fly, narcissus, hyacinth, onion and shallot. These flies
are two-winged insects, the hind wings being wanting as such, and
belong to a group called the syrphid, or hover flies.
The larger narcissus fly (Fig. 12, h1) resembles somewhat a humble-bee
(which, however, has four wings); its stout and very hairy body
measures about half an inch long. There is considerable variation in
colour, though black or brown predominates, with greyish or yellowish
hairs, and bands of the same colour; the bands, however, are absent in
some individuals.
During spring the insects fly about in the sun, and lay their eggs at
the leaf bases of the host plants, or on the exposed neck of bulbs, or
in the soil close by. The larvæ, which are legless, yellowish grubs,
enter the bulb, and may completely destroy it. Infested bulbs may be
detected by an unnatural softness near the neck when pressed between
the fingers.
The smaller narcissus fly (Fig. 12, h2) is about half the length of
the larger, of a shiny black colour, with metallic reflections, and is
not clothed with hair. The eggs are laid in the ground, or at times
upon the plant itself. Several larvæ of this fly may be found in the
one bulb; the larvæ resemble those of the larger fly, but are smaller,
and have three small processes at the end of the body. The smaller
narcissus fly usually attacks the bulbs already damaged by some other
agent, though it has been known to infect sound bulbs.
Control of both these flies depends upon the destruction of infested
bulbs. Recent researches have shown that the flies themselves can be
poisoned in large numbers by a spray made of 4oz. of sodium arsenate,
1lb. of crude glycerine, 2lb. of white sugar, and four gallons of
water; this spray is applied during bright and warm weather.
SPRINGTAILS.--These are very minute, soft-bodied insects, which
are very active, and have a habit of springing with the agility of
fleas. There are several species, but two are of interest to the
horticulturist.
One of these (Fig. 12, k1) is white in colour, narrow-bodied, and lives
underground, especially in damp places, where it damages germinating
seeds, or the roots of seedlings; even older herbaceous garden plants
are attacked. As a control, it is important to drain the soil in damp
locations and to dig in calcium cyanide about two weeks before planting
or sowing.
The second species is blackish and more or less spherical (Fig.
12, k2); at times it does considerable damage in the spring to the
seed-leaves of young plants as soon as they appear above ground.
Spraying small areas--_e.g._, of cucumbers, turnips, etc.--with
black-leaf 40 would help to protect the plants; as the eggs are laid in
the ground, and as these develop best under moist conditions, thorough
cultivation prior to sowing the crop is an important controlling
factor.
CHAPTER IX.
Miscellaneous Pests.
In this chapter will be grouped for convenience mites, woodlice,
millepedes, slugs, snails, and eelworms.
Mites.
Mites, together with spiders and ticks, belong to a group of animals
distinct from the insects, from which, they differ in many respects;
for example, they possess four, and not three, pairs of legs in the
adult state, no head separated from the body as a movable, distinct
region, while in many cases, especially in mites and ticks, the abdomen
and thorax are continuous; in no case are wings developed.
Mites are of small size, some being microscopic, while others are
just discernable by the unaided eye. All species have the mouth-parts
developed for the purpose of feeding upon liquid food--_e.g._, blood
(in the case of those species that attack animals), decaying vegetable
matter, or the saps of plants. It is the last--that is, those parasitic
upon plants--with which we are here concerned.
The life-history of mites presents some variability, and, though
there are fundamentally four stages of development, additional stages
have been developed by some species which tend to complicate the
cycle. The principal stages in development are as follows (Fig. 13,
1-5):--In practically all cases eggs are deposited, but few species
being viviparous. The larva, on hatching, possesses but six legs, and
resembles an insect in this respect; the larva then becomes quiescent,
and after moulting the eight-legged nymph appears. While in the
nymphal state the mite may undergo one or more moults, giving rise to
additional nymphal forms, that may complicate the life-history. From
the final moult of the nymph the adult mite emerges.
Perhaps the best-known mite in New Zealand is the European red mite
of apple trees (_Paratetranychus pilosus_), though it attacks a wide
range of plants apart from deciduous fruit trees, which it favours; it
has been found on grape vine, raspberry, rose, hawthorn, citrus, etc.
This mite (Fig. 13, 6) occurs in Europe, Russia, British Isles, North
America, Australia, and New Zealand, and it causes considerable injury
to foliage, which assumes a brown appearance, owing to the tissues
drying up where they have been punctured by the mouth-parts of the mite.
In the case of heavily-infested trees, the red eggs of this mite form
conspicuous patches on the bark during winter; these winter eggs are
laid from January onward till leaf-fall, and from them the young mites
hatch in the spring, when the foliage is again attacked. The red mite
develops rapidly, and reaches the adult stage in about two weeks;
several generations are thus produced from spring to autumn, when the
eggs are laid upon the foliage.
The eggs (Fig. 13, 7) are very small, globular, and ribbed on the
surface; from the centre of each projects a hair-like stalk, somewhat
bent at the tip. The colour is bright red, changing to a deep orange.
The red mite lives freely upon the foliage, and does not produce a
web, as do related species; the adult female is bright red to dark
brownish-red, rather globular in shape, with comparatively stout legs
and numerous spine-like hairs on the back. Although the eggs of the
European red mite are exposed on bark and readily accessible to sprays
during the winter, no effective winter wash for their control is yet
known; the most satisfactory method for checking the pest is to spray
the active stages of the mite with summer oil.
Another species of mite, having much the same habits and host plants
as the European red mite, is the brown mite (_Bryobia prætiosa_). The
eggs of this species are of a deep red, with a yellowish tinge in many
cases, but differ from those of the European red mite in the absence of
the polar-stalk and ribbed surface. The brown mites (Fig. 13, 8) are of
a dull red or greenish colour, lack the spine-like hairs on the back,
are decidedly flattened, and have the front pair of legs abnormally
long.
The common red spider (_Tetranychus telarius_) is a species of mite
frequently met with on a wide range of plants too numerous to mention
here; in New Zealand it frequently injures violet, hop, currant,
willow, and many weeds. This mite is to be found in all stages
practically all the year round; during the spring it is mostly found
on weeds and such cultivated plants as strawberry and violet. It is a
web-spinning species, and the minute yellowish-red eggs are to be found
scattered among a fine web attached to the lower surface of leaves as a
rule. The adult mite (Fig. 13, 9) is very active; it is somewhat larger
than the two foregoing species, and of a yellowish-green colour, with
a pair of conspicuous dark spots on the back. Though this mite can be
held in check by the application of lime-sulphur sprays, advantage
should be taken of thorough cultivation during the dormant season,
since the mite hibernates on weeds and among dead leaves and in the
soil.
A mite very often met with by bulb growers is the bulb-mite
(_Rhizoglyphus hyacinthi_), now found in most parts of the world.
Although this mite may possibly be able to attack practically all
tubers or bulbs, it is commonly found infesting narcissus, hyacinth,
tulip, crocus, and Easter lily; it is especially abundant in bulbs with
loose scales, and has been found to be capable of attacking healthy
tissue. The life-history of this species is complicated at times by
the development of additional stages; one of these--the hypopus--is of
particular interest, as it shows more activity than the others, and
attaches itself to the bodies of insects, and is so transported. The
mite develops from egg to adult within a period of nine days under
favourable conditions, or as long as six weeks at other times. All
stages of the bulb-mite occur at the same time in infested bulbs, which
become soft and rotten. The adult mites (Fig. 13, 10) are smooth,
yellowish-white, tinged with pink, and have legs and mouth-parts
reddish. Symptoms of their presence are to be found in stunted growth
and yellowing leaves, failure of flower development, reddish spots on
bulb scales, or a softening of the bulbs. All seriously-infested bulbs
should be destroyed, and the ground where they were grown treated with
calcium cyanide. For the treatment of bulbs, they should be immersed
for ten minutes in a two per cent. solution of formalin heated to 122
deg. Fahr., or simply in water at a temperature of 131 deg. Fahr.
[Illustration: FIG. 13.
(1) Five stages in mite development: (1) Egg, (2) larva, (3) nymph, (4)
older nymph, (5) adult mite. (6) European red mite and (7) egg of same.
(8) Brown mite. (9) Common red spider. (10) Bulb mite. (11) Pear-leaf
blister mite. (12) Common woodlouse. (13) Garden millepede. (14) Garden
slug. (15) Garden snail. (16) Bulb eelworm. (17) and (18) Immature
and mature beet eelworm. (19) and (20) Immature and mature root knot
eelworm.]
Another group of mites of importance to the horticulturist is
that of the blister mites; they are so minute--measuring about a
hundred-and-fiftieth of an inch long--as to be invisible to the
unaided eye. Though so minute, however, their damage to foliage is
characteristic and conspicuous, so that their presence is easily
detected. The most important blister mite in New Zealand is the
pear-leaf blister mite (_Eriophyes pyri_); it differs from the other
mites described above in having a long and cylindrical body, with only
two pairs of legs crowded at the head end, the elongate abdomen having
the appearance of being composed of innumerable segments (Fig. 13,
11). This mite lives in colonies in blisters formed on the leaf, and
sometimes on the leaf petioles. In the spring the yellowish-green
blisters will give the upper surface of an infested leaf a spotted
appearance, and as the season advances these blisters become reddish
and finally brown; in the case of severe infestation, the blisters
become so crowded as to merge into masses.
During the winter the mites lie in the shelter of the bud scales; as
soon as the foliage begins to develop in the spring the over-wintering
mites attack the leaves, each mite forming a blister, in which it
produces a colony of young. The offspring then migrate from the parent
blister and form blisters for themselves, and this goes on until
autumn, when the last generation of mites migrates for the winter to
the shelter of the bud scales.
Owing to the mites being protected within the leaf blisters, summer
sprays are not effective as a means of control, which can be effected,
however, by spraying with lime-sulphur in the autumn, when the mites
are taking up their winter quarters, and again at bud movement in the
spring.
Woodlice.
Woodlice are so well known, that but little description is necessary
here. However, the following features are of interest. They belong to
the group of animals known as the _Crustacea_, which also includes
the crabs; these animals breathe by means of gills, and are usually
aquatic, but some forms, such as the woodlice, have become adapted to
a life on land. In outline (Fig. 13, 12) the woodlice are more or less
oval, with the upper surfaces somewhat arched, and the lower flat; the
body is divided into several segments, which may enable the animals
to curl up in the form of a pill. There is a distinct head, bearing a
pair of antennæ and the mouth-parts, followed by seven large thoracic
segments, to each of which a pair of legs is attached; finally,
the remaining six segments are more or less crowded together, and
constitute the abdomen.
Since woodlice are terrestrial gill-breathing animals, moisture is
essential for them, and it is in moist places that they abound. They
depend upon a mixed diet, being carnivorous, as well as herbivorous;
though normally scavengers, their attacks upon seedlings and tender
parts of plants bring them into the ranks of important garden pests.
Woodlice hibernate under any convenient shelter; in the spring, eggs
are produced and carried by the female on the under side of the body
until the young woodlice hatch. During growth the cuticle or shell is
periodically cast, and a freshly-moulted woodlouse is white in colour.
The best method of control is garden sanitation, all rubbish likely
to harbour the woodlice being removed. Since they are nocturnal, the
woodlice can be trapped by means of moss laid on the ground; the moss
in which the woodlice have taken shelter is collected during the day
and burned, or immersed in hot water to kill the animals, when it can
be used again. Some good results have been secured by means of sliced
potatoes dipped in arsenate of lead or Paris green; the potatoes are
placed within reach of the woodlice, which are attracted to and feed
upon the poisoned bait. Horse manure should not be used in seed beds
likely to be infested by woodlice.
Millepedes.
Millepedes are short, worm-like animals, with a fringe of numerous
short legs on each side (Fig. 13, 13), and have a characteristic habit
of curling up when disturbed. Though scavengers for the most part,
feeding upon decaying vegetation and on small organisms, they may
do considerable damage to sprouting seeds, seedlings, and to tender
plants; they are particularly abundant in damp and warm soil, where
there is an abundance of rotting vegetable matter.
Having a keen sense of smell, millepedes are readily attracted to
poisoned bait in the form of sliced potato spread with Paris green:
another method is to place a piece of freshly-cut potato under an
inverted flower pot, to which the millepedes will be attracted, when
they can be collected and destroyed. A satisfactory control measure
is to treat infested soil with black-leaf 40, using one part in one
thousand parts of water.
Slugs and Snails.
Plants are very often greatly damaged by the depredations of slugs and
snails; frequently young plants are devoured as soon as they appear
above ground. These animals attack the plants after nightfall, and
during the day seek cover. Though slugs will shelter in the soil,
they, together with snails, will shelter in any convenient place,
such as under old boards, sacking, bricks and stones upon the ground,
or under large leaves or amongst rank herbage--indeed, in almost any
place that affords cover and moisture. Slugs and snails are especially
active during wet weather, and at such times, owing to the overcast
conditions, they will continue their depredations in the daytime.
Though slugs are active throughout the year, and even during winter
when the temperature is favourable, snails pass the winter, as well
as hot, dry spells in summer, in a dormant state, often being found
together in sheltered positions where the conditions are dry.
Both slugs and snails copiously secrete a slimy substance, that affords
them protection against chemicals used for purposes of control. In the
case of the slug (Fig. 13, 14), the shell is small and inconspicuous,
but the large spiral shell of the snail (Fig. 13, 15) affords the
animal adequate protection, into which it withdraws itself in times of
danger. Both slugs and snails reproduce by means of eggs; these are
white, spherical and opaque, and are deposited in the soil or under
decaying vegetation.
One of the best means of control is to dust the plants with powdered
tobacco. Another method is to treat infested plants with soot or lime,
but this must be done at night, and the material used must come into
actual contact with the pests. An effective poison bait, but one that
requires to be carefully handled, owing to its poisonous nature, is a
mash made of 6lb. of bran mixed with 1lb. of arsenate of lead and an
equal weight of treacle; this is made into a stiff paste, water being
added if necessary. Lumps of this mash are placed about the plants to
be protected. As a barrier to prevent the inroads of slugs and snails,
plants may be surrounded by a belt of calcium cyanide; this would have
to be replaced each night, and the utmost care taken in handling, since
the substance and the gas evolved from it are highly poisonous; out
of doors, however, the gas, being diluted with air, would not be very
injurious as long as one did not stand over the treated ground longer
than was necessary for laying the cyanide.
Apart from the above methods, the key to the control of slugs and
snails is “clean farming”--that is, the removal of all places, such as
rubbish and rank vegetation, where the animals will find shelter; the
compost heap is a favourite breeding place, and this should be turned
over at intervals and dressed with lime.
Eelworms.
Eelworms are minute, unsegmented worms, related to the parasitic
thread-worms of animals, and are abundant in soil and water; it is
usually the surface layers of the richer soils that are inhabited
by them. Of the long list of species, only a few are destructive to
vegetation, but these constitute one of the greatest problems of the
horticulturist. It is thought that the injury caused to plants by
eelworms is toxic rather than mechanical, and some plants apparently
are capable of producing anti-toxins, which neutralise the toxins
of the eelworms; such plants possess an immunity. There are three
important species in New Zealand.
The so-called bulb-eelworm (_Anguillulina dipsaci_) attacks more
than two hundred kinds of plants, but is of especial interest to the
horticulturist on account of its attacks upon hyacinths, daffodil,
narcissus, and gladiolus, causing deformity and rotting of the tissues
(Fig. 13, 16). It has been found that this eelworm develops from egg
to adult within a period of between three and four weeks; the eggs
are capable of lying dormant in the soil for as long as seven years.
Infested bulbs and corms should be treated by immersion for three hours
in water heated to 110 deg. Fahr.
Potatoes are often damaged by the beet eelworm (_Heterodera
schachtii_), which causes what is known as “potato sickness,” when the
growth is retarded, and wilting takes place; the root-system shows an
abnormal development of secondary or “hunger-roots.” The eggs are
retained in the body of the female, which forms a protective sack or
cyst (Fig. 13, 17 and 18), and in this state the eggs pass the winter
in the ground, where they are known to remain dormant for a period of
ten years; under favourable conditions in the spring, the larvæ emerge
from the eggs and attack the rootlets of suitable host plants, entering
them at the extreme tip. Satisfactory methods of control have not yet
been developed under field conditions, but a four-year crop rotation
following potatoes is suggested; seed potatoes from infested ground
should not be used.
The roots of tomatoes are often found to be a mass of galls, due to
attack by the root-knot eelworm (_Heterodera radicicola_), which also
infests tobacco roots as well as other plants (Fig. 13, 19 and 20). All
stages of this species are to be found in the root galls; the female
lays her eggs in a gelatinous egg sack, which remains attached to the
parent. The larvæ, on hatching, either remain within the parent gall or
leave it and enter the soil, where they seek out and attack the roots
of another plant. In tomato gardens steam sterilisation of the soil is
the most effective means of control.
CHAPTER X.
Principles of Pest Control.
In dealing with the control of plant pests, the objective is to prevent
attacks, or, when the attacks have established, to check them as much
as possible. In the latter case the term “exterminate” is in too
frequent use; it is not usually practicable to exterminate a pest, and
the best that can be done is to check or control it.
In the control of animal pests, it should be borne in mind that the
pests are usually associated with other factors inimical to plant life,
such as unthrifty plants, due to injury or malnutrition, and fungous
and bacterial diseases, any one of which might be either the primary or
secondary cause of plant injury.
Though at times one method may serve as a means of control, generally
it is a combination of methods that gives the most satisfactory
results, rendering the conditions favourable for the plant and
unfavourable for the pests and diseases. The principles underlying
control are:--
(_a_) Garden management.
(_b_) Use of chemicals.
(_c_) Influence of natural enemies.
(a) Garden Management.
All parts of plants, both above and below ground, are subject to
infestation by pests and diseases. Under garden conditions, cultivation
is intensive, and plants are grown year after year on the same ground
in surroundings much more sheltered and crowded than in the open field.
Sound garden management is therefore an important control factor, and
the following features are fundamental:--
CONDITION OF SOIL.--The vigour of plants is dependent on the soil,
which therefore must be kept in the right state; it must be well
tilled, and must contain the requisite nourishment and moisture
available for plant use, and as far as possible be free of an abnormal
population of root feeding pests, such as eelworms and the larvæ of
many insects. Proper cultivation is therefore the important factor in
bringing the soil into the state most favourable to plant life, as all
inimical factors, including pests, are reduced. Wherever practicable,
as in glass-houses, soil-inhabiting pests and diseases can be
completely controlled by steam sterilisation.
IMPORTATION OF PESTS.--One of the readiest methods of infesting a
garden is the importation of pests on plants, and every care should
be taken to secure only pest-free stock. In this respect, also, must
be mentioned the use of stable and barnyard manure, in which pests
such as insect larvæ, woodlice and eelworms are introduced; artificial
fertilisers are therefore safer.
OVERCROWDING.--The tendency to overcrowd, especially in household
gardens, is to be avoided; a favourite habit is to plant something
in every available space. Under such conditions pests and diseases
will abound, and before attempting to spread over a large area, and
so lessen the effect of their depredations, they concentrate in mass
formation within the confines of the garden as long as the food supply
lasts; further, plants tend to be less vigorous and more susceptible to
infestation under crowded than under more open conditions.
INJURY TO PLANTS.--Care should be taken not to injure plants with
garden tools during cultivation, and a clean cut should always be the
object in pruning. Mechanical injury opens the way for infestation by
diseases and some insects.
GARDEN SANITATION.--Clean gardening is an extremely important control
factor. In most gardens there are rank growths of grass and weeds in
out-of-the-way places, along boundaries, and bordering cultivated
plots. Such growths, especially when the weeds are related to the
garden plants, are always favourite breeding places for many pests that
move on to cultivated plants immediately they appear above ground.
If these growths are cut and burned in the winter, and the ground
thoroughly dug, many a spring infestation will be suppressed by the
control of hibernating pests; it is the control of spring infestations
that will save a great deal of trouble throughout the summer and autumn.
The compost heap, where garden refuse is dumped until sufficiently
rotted, may be a source of infestation; not only does it attract and
breed many destructive underground pests, but it may be infested with
the spores of diseases harboured by the plant refuse of which it is
composed; it is thus a ready means of reinfesting the soil. Diseased
and pest-infested refuse should be burned without delay, and only
healthy refuse used for the compost heap if not dug into the ground,
where it will rot.
CROP ROTATION.--Growing the one type of crop on the same piece of
ground for several seasons encourages the development of pests and
diseases; but by a rotation of different kinds of plants the continuity
of the conditions favourable for the pests and diseases is broken, and
the latter do not have the chance of becoming thoroughly established.
DISEASES SPREAD BY PESTS.--It should be borne in mind that the fewer
the animal pests, the less chance there is for diseases to spread. It
is now well known that many pests, though not necessarily epidemic
themselves, are carriers from plant to plant of certain destructive
fungous, bacterial and virus diseases.
CO-OPERATION.--In a locality of many gardens a co-operative spirit is
essential, since a single neglected garden in an otherwise well-managed
locality will be responsible for discounting the labours of the
neighbours.
(b) Use of Chemicals.
Chemicals are essential in the control of pests and diseases, and
are applied either in the form of sprays or dusts. The former method
is the more usual in this country, but where the water supply is
poor dusts tend to take the place of sprays. Chemicals used for
horticultural purposes are of two distinct kinds--those for the control
of animal pests and those for the control of diseases. The commercial
horticulturist, however, finds it necessary to apply both in the one
spray or dust for the dual purpose of controlling both pests and
diseases. As the present work is concerned with the pests, and not
diseases, only those types of chemicals for the control of the former
will be referred to.
Sprays and dusts are of three kinds, and act upon pests accordingly:
they are either stomach poisons, or act externally on the animal by
actual contact and corrosion, or cause death by fumigation. The kind
used is governed by the feeding habits of the pest; if the latter is
possessed of jaws (woodlice, caterpillars, beetles, etc.), and feeds
by chewing the plant tissues, then a stomach poison is applied and is
swallowed with the food; if the food is the nutrient sap of plants,
and so could not be poisoned, a spray acting by contact is used, as
against such animals as aphids (green fly), scale insects, etc., in
which the mouth-parts are not adapted for chewing, but for puncturing
plant tissues to feed on the sap, much the same as a mosquito punctures
one’s skin and sucks the blood. Fumigants can be used against both the
chewing and sucking pests, the fumes passing into the breathing system.
STOMACH POISONS.--The chief of these are arsenate of lead and Paris
green, though the latter has practically gone out of use. Arsenate of
lead is sold as a paste and as a powder, and is mixed with water to
form a spray, 3lb. of paste, or 1-1/2lb. of powder, to 100 gallons
of water being the proportions used. For garden purposes, smaller
quantities must be kept to this strength.
CONTACTS.--The chemicals used in contact control are red oil, kerosene
and lime-sulphur, but all are also fumigants, lime-sulphur being also a
stomach poison to a limited extent, though best known as a fungicide.
Commercial red oils can be purchased ready for mixing with water
without the necessity of emulsification, and the strength at which each
brand should be used is given by the manufacturers. Though red oils
have mostly replaced kerosene emulsion, many horticulturists still
prefer the latter. It is prepared by dissolving 8oz. of soap in one
gallon of hot water, and then adding two gallons of kerosene, stirring
briskly until emulsification is complete. This is the stock emulsion,
and must be diluted before use, the strengths being one part to six of
water for use in the winter, and one part to fifteen of water for use
in the growing season. Commercial brands of concentrated lime-sulphur
are on the market, and the manufacturers’ directions for their dilution
should be followed.
FUMIGANTS.--The chief fumigants are black-leaf 40, carbon-bisulphide
and calcium cyanide.
Black-leaf 40, in which nicotine sulphate is the effective principle,
is the most useful fumigant on the market, and acts as a most effective
control for sap-sucking, and even some chewing pests. The strength at
which this fumigant is used is one part in 800 parts of water, and is
applied as a spray.
Carbon-bisulphide is a liquid, the gas evolved from it being an
effective fumigant. It is not used as a spray unless emulsified,
its chief use in horticulture being for the fumigation of the soil,
glass-houses, stored seeds and vegetables, and imported plants. It
is very inflammable and extremely volatile, especially under higher
temperatures, the heavy gas being highly explosive when mixed with air.
The amount of carbon-bisulphide to be used varies, according to
circumstances. For soil fumigation a special type of “gun” is on the
market for injecting the bisulphide into the soil, but for ordinary
garden purposes it is sufficient to make holes in the ground with a
stick, pour in the fumigant, and close up the holes. When holes are
made about 18 in. apart, half an ounce of bisulphide to a hole is
sufficient, the depth of the hole varying according to the depth of the
pest to be controlled.
For the fumigation of seeds, bulbs, potatoes, etc., an airtight chamber
is necessary. This is also of value in the control of pests of potted
plants. The dimensions of a chamber will vary according to the demands
made upon it. Carbon-bisulphide gas being heavy, the containers
(shallow dishes) should be placed on a shelf near the top of the
chamber during fumigation. The proportion of fumigant to the air space
varies according to the plants and insects to be fumigated.
For lawn-infesting insects, carbon-bisulphide can also be used in an
emulsion as a spray prepared as follows:--Fifty grams of powdered
resin are gradually added to 135 cc. of a 7 per cent. solution of
sodium hydroxide, previously warmed; 450 cc. of hot water is now added,
and the whole agitated until the resin is completely dissolved, when
50 cc. of oleic acid is also added. To prepare the emulsion, three
parts of this soap solution are thoroughly agitated with seven parts
of carbon-bisulphide until emulsification is complete, which can be
gauged by the creamy-white colour and viscosity. For use dilute in
the proportions of 18 pints of the emulsion with 50 gallons of water,
applying by means of a watering-can or spray-pump at the rate of one
gallon to every square foot of lawn.
Calcium cyanide, on being exposed to the atmosphere, gives off
hydrocyanic acid gas, the evolution of the gas being governed by
temperature and humidity. Calcium cyanide has replaced the old method
of generating the gas by the action of sulphuric acid on potassium
cyanide, and is sold in the form of dusts or granules. In the use of
this material very great care is necessary, since the gas is highly
poisonous, and also scorching of the foliage of plants results if
atmospheric conditions are not considered carefully. With ordinary
care, however, calcium cyanide can be safely handled. It is extremely
effective against all kinds of pests, and can be used to fumigate soil,
glass-houses, or as a dust on plants in the open.
(c) Influence of Natural Enemies.
As stated in the first chapter, plants are to be looked upon as the
primary producers of life (since all animals are directly or indirectly
dependent upon them), and the animals as the consumers. Many of the
latter are destructive to crops grown by man, and become pests, but
others, fortunately, exist upon these pests, and are classed as
beneficial animals; it is the purpose of this section to deal with the
more important of these from a horticultural viewpoint. In New Zealand
such beneficial animals are insects, birds, and the hedgehog.
Insects.
There is a wide range of insects that live at the expense of their
fellows, and without these plant production would be impossible, either
by Nature or by man. These so-called beneficial insects or parasites
are the greatest factor in maintaining within reasonable bounds the
insects that destroy vegetation; they are of much greater value in this
respect than birds. In recent times the utilising of beneficial insects
as a means of pest control has developed as one of the most important
branches of entomological research.
From a general viewpoint, the beneficial insects are to be found mainly
among the groups, including wasps, beetles, flies (two-winged insects)
and lace-wings. The following are some examples:--
Common examples of parasitic insects are the ichneumon wasps
(Fig. 14a), chalcid wasps (Fig. 14b), and ensign wasps, the first being
the most conspicuous, the others less so owing to the minute size of
many of them. A characteristic feature of these forms is the stalk-like
attachment of the abdomen to the thorax and the sting-like ovipositor
of the female, which may be of short or moderate length, sometimes
projecting as a tail-like appendage beyond the end of the abdomen.
Parasites deposit their eggs either upon or within the body of their
victims or hosts, which are eventually destroyed by the larvæ hatching
from the parasites’ eggs. Destructive caterpillars and their pupæ, and
also aphides, are attacked by these wasp-like parasites, which in many
cases restrict their depredations to one or a limited number of host
species, while others are more general in their selection. Another
group, the predaceous wasps, should be mentioned here. These insects in
the adult state are hunters, and capture and paralyse by stinging such
insects as caterpillars and flies, as well as spiders, which are stored
in nests or cells for the nourishment of the predators’ offspring.
Important natural enemies of aphides and young caterpillars are the
hover-flies, which can be easily recognised by their manner of flight.
They are two-winged insects (Fig. 14c), and when on the wing hang
motionless, as if suspended by some unseen means, to suddenly dart off
with marvellous rapidity, until they hang motionless as before. These
flies lay their eggs upon the foliage of plants infested by aphids or
caterpillars, and from these eggs legless and headless larvæ emerge
(Fig. 14d), and commence to search for and feed upon their victims.
Another important group of two-winged flies is the tachinids. They
are rather robust, usually very bristly (Fig. 14e); they vary in size
from that of a large blue-bottle to comparatively minute forms. The
tachinids lay their eggs either upon their hosts or on the food plants
of the latter, where they can be swallowed; some tachinids give birth
to living larvæ, which crawl about in search of their victims.
Among the beneficial beetles are the well-known ladybirds (Fig.
14f); they are mostly oval in outline, dome-shaped above and flat
below, while many of them are spotted by yellow, red, or white in a
characteristic manner, though others are of one uniform colour. The
eggs are laid on plants infested by the aphides and scale insects
upon which the beetles and their larvæ (Fig. 14g) feed. There are
other kinds of beetles of importance as predators, such as the common
tiger-beetle, but they are not especially selective in their types of
victims.
A very valuable group of insects includes the lace-wings or
aphis-lions. The adult insects (Fig. 14h) carry the seemingly
over-large lace-veined wings roof-like over the small body; the larvæ
are alligator-like (Fig. 14i), and possess a pair of caliper-shaped
jaws, by means of which they capture their prey. The eggs are laid
directly on plants or are attached at the end of long stalks.
Birds.
It is generally recognised that birds are a very important aid in
keeping destructive insects in check, though it is well-known that a
great deal of damage can be done by these animals. Without a systematic
study of the stomach contents of birds, it is not possible to decide
when a species is beneficial or injurious, and in New Zealand no such
study has been made; practically all the information we have is based
on field observations, which are, unfortunately, influenced largely
by the outlook of the observer, and are thus misleading. Though some
species subsist for the most part on insects, most land-birds have a
mixed diet of vegetable and animal food, but they specialise on an
insect diet when rearing their young and when moulting.
[Illustration: FIGURE 14.
(a) An ichneumon (natural size 1-1/4 in); (b) a chalcid (natural size
1-25 in); (c) a hoverfly (natural size 1/8 in); (d) hoverfly larva
(natural size 1/4 in); (e) a tachinid fly (natural size 1/4 in); (f)
a ladybird beetle (natural size 1/5 in); (g) ladybird larva (natural
size 1/4 in); (h) lacewing (natural size 1/4 in); (i) lacewing larva
(natural size 1/5 in).]
Based on the nature of their diet, birds fall into three principal
groups: (1) those feeding almost solely upon seeds and fruits; (2)
insectivorous birds feeding on insects and other animals; and (3) the
omnivorous species feeding both on insects and vegetable matter. The
seed-feeding birds are a potential menace to the agriculturist, though
in New Zealand the native species are fundamental to the well-being of
the native forests; the insectivorous birds are obviously beneficial,
though they devour both destructive and useful insects; while the
omnivorous birds may be either useful or harmful, according to the
circumstances. It should be remembered that, no matter what the food of
the adult bird may be, most species give their young a diet of insects
or other animal matter. When it is realised that the weight of nestling
birds increases from one-fifth to one-half each day, requiring at times
more than half the weight of the nestling in food, one can better
visualise the enormous quantities of insects daily destroyed for this
purpose. Consider the common house sparrow, which is usually condemned:
an analysis of the nestling diet has shown that it consisted of 40 per
cent. grain and 60 per cent. insects and related forms, while that of
the adult comprised 75 per cent. grain and 25 per cent. insects, etc.
To summarise the situation, it may be said that, on the whole, enormous
numbers of insects are destroyed by birds each year, and, unless
allowed to become abnormally abundant, the benefit derived from birds
outweighs the damage they may cause.
Hedgehog.
The hedgehog was first introduced by the Canterbury Acclimatisation
Society in 1870, and later by other societies and private individuals.
The animal is now very abundant in many parts of the Dominion. Though
condemned and destroyed by some people, who consider it a menace to
eggs, chickens and even vegetables, the hedgehog is really a very
useful animal, in that, being a night prowler itself, it destroys
numerous nocturnal pests, such as slugs and snails, earwigs, grass
caterpillars and cut-worms.
The hedgehog, on the approach of winter, constructs a nest in some
suitable place, where it becomes torpid and hibernates. On the advent
of spring, it becomes active once more, and during summer produces a
litter of four young; a second litter is sometimes produced in the
autumn.
INDEX.
Page
Acacia, 32, 38
_Agrotis ypsilon_, 52
_Algæ_, 14, 15
Almond, 35, 38, 64
Amaryllis, 66
American blight, 47
_Amœbæ_, 15
_Anguillulina dipsaci_, 72
Animal Kingdom, Divisions of, 8
_Aphelinus fuscipennis_, 40
_Aphelinus mali_, 47
_Aphelinus mytilaspidis_, 38, 40
Aphides, 42
Aphis-lion, 28, 78
_Aphis persicæ-niger_, 44
Apple, 34, 35, 37, 38, 40, 41, 47, 48, 61, 64, 67
Apple leaf-hopper, 48
Apple leaf-roller, 51
Apple mealy-bug, 34
Apple mussel-scale, 30, 37
Apple red-mite, 57
Apricot, 35, 36, 38
Army-worms, 54
Arsenate of lead, 76
Asexual, 42
Ash, 38
Asparagus, 36
_Aspidiotus hederæ_, 40
_Aspidiotus perniciosus_, 38
_Asterolecanium variolosum_, 37
Austrian pine, 46
Bacteria, 14, 15
Bag-moth, 56
Baker’s mealy-bug, 35
Beet eelworm, 72
Beetles, 56
Begonia, 34
Beneficial insects, 77, 78
Birds, 79
Blackberry, 36, 41
Blackbird, 35
Black cherry-aphis, 44
Black-currant, 36, 44
Black-leaf 40, 76
Black peach-aphis, 44
Black scale, 40
Blister-mites, 70
Blue-gum, 59
Borers, round-headed, 64
Breathing systems of insects, 21
_Brevicoryne brassicæ_, 45
Briar, 41
Bronze beetle, 58
Broods of insects, 22
Broom, 52
Brown-beetle, 58
Brown-mite, 68
Brussels sprouts, 45
_Bryobia prætiosa_, 68
Bulb-eelworm, 72
Bulb-mite, 68
Bulb or Narcissus flies, 66
Cabbage, 45, 48, 55
Cabbage aphis, 45
Cabbage green-fly, 45
Cabbage-tree, 56
Cabbage-tree moth, 56
Cabbage-tree scales, 38
Cabbage white butterfly, 55
Calcium cyanide, 76
_Caliora limacina_, 59
Camellia, 35, 36, 37, 40
Camellia scale, 37
Carbon-bisulphide, 76
Caterpillars, 51
Caterpillars in lawns, 65
Cauliflower, 45, 55
_Cecidomyia oleariæ_, 60
Cereals, 54
Chalcid wasps, 78
Chemicals, 75
_Chermes pini_, 46
Cherry, 38, 44, 59
Cherry-aphis, black, 44
Cherry slug, 59
Chitin, 17
Chrysalis, 25
Chrysanthemum, 64
_Chrysomphalus aurantii_, 40
_Chrysomphalus rossi_, 40
Cicada, 28
Cineraria, 24, 34, 56, 64
Citrophilus mealy-bug, 34
Citrus, 32, 35, 36, 40, 64, 67
Click-beetles, 65
Clover, 52
Coccids, 29
_Coccus hesperidum_, 36
Cockchafers, 57
Cockroach, 17, 27
Cocoon, 25
Codlin moth, 61
Comstock’s mealy-bug, 35
Contact sprays and dusts, 76
Convolvulus, 54
Coprosma, 40
Cornicles, 42
Cottony-cushion scale, 30, 32
Crayfish, 17
Crickets, 27, 51
Crocus, 68
Crop rotation, 75
Cruciferous crops, 45
Cryptolæmus ladybird, 34
_Cryptolæmus montrouzieri_, 34
Curl-grubs, 58
Currant, 37, 38, 61, 68
Currant clear-wing borer, 61
Cuticle, 17
Cut-worms, 52
_Cydia pomonella_, 61
Daffodil, 72
Development of insects, 22
Diamond-backed moth, 52
Digestive system of insects, 21
Douglas fir, 32, 46
Dusts, 75
Earthworms, 15
Earwig, 27, 50
Easter lily, 68
Eelworms, 8, 72
Eggs of insects, 22
Elder, 35
Eleagnus, 37
Elm, 38, 47
Elm-leaf aphis, 42, 47
Elytra, 58
Ensign wasps, 78
_Eriococcus coriaceus_, 35
_Eriophyes pyri_, 70
_Eriosoma lanigerum_, 47
Eucalypts, 35, 59
Eucalyptus tortoise beetle, 59
_Eucolaspis brunneus_, 58
_Eulecanium berberidis_, 37
_Eulecanium corni_, 36
_Eumerus strigatus_, 66
Euonymus, 35, 37, 40
European earwig, 50
European red-mite, 67
Fantail, 35
Ferns, 34, 36
Fig, 34, 35, 36, 40
Flax, New Zealand, 38
Flea-beetles, 58
_Forficula auricularia_, 50
Fruit lecanium scale, 36
Fumigants, 76
Fungi, 14, 15
Galls, 42
Galtonia, 66
Gladiolus, 72
_Gnorimoschema plæsiosema_, 62
Goat-willow, 64
Golden oak-scale, 37
_Gonipterus scutellatus_, 59
Gooseberry, 35, 36, 37, 38, 64
Gorse, 32
Grape louse, 46
_Grape phylloxera_, 46
Grape-vine, 34, 35, 36, 37, 40, 46, 51, 67
Grass caterpillars, 65
Grasses, 64, 65
Grass-grubs, 57, 64
Grasshopper, 17, 51
Greasy cut-worms, 52
Green-fly of cabbage, 45
Green-house thrips, 49
Green-house white-fly, 48
Green manuka beetle, 58
Green peach-aphis, 44
Groundsel, 24, 56
Grub-proofing lawns, 64
Gum-tree scale, 35
Gum-tree weevil, 59
_Habranthus_, 66
_Habrolepis dalmanni_, 37
Hawk moth, 54
Hawthorn, 37, 38, 59, 67
Hedgehog, 80
_Heliothrips hæmorrhoidalis_, 23
Hemispherical scale, 36
_Heterodera radicola_, 73
_Heterodera schachtii_, 72
Hibernation, 23
Holly, 35, 36
Honey-bee, 19
Honey-dew, 29, 42
Honey-tubes, 42
Hop, 68
Horse chestnut, 35
Hover-flies, 66, 78
Hyacinth, 66, 68, 72
Hydrangea, 35
Hydrocyanic-acid gas, 77
_Hypopus_, 68
_Icerya purchasi_, 32
Ichneumon wasps, 78
Importation of pests, 74
Insects, proportion of, 7
Insignis pine, 46, 51
Invertebrates, 7
Iris, 35
Ivy, 35, 36, 40
Japonica, 36
Karaka, 40
Kerosene, 76
Kowhai, 52
Kowhai moth, 52
Kumara, 54
Lace-wing, 34, 78
Ladybird beetles, 78
Larch, 46
Larger narcissus fly, 66
Larva, 24
Laurel, 35, 36
Lawns, 64, 65
Lead arsenate, 76
Leaf-hoppers, 48
Leaf-mining flies, 64
Leaf-rollers, 51
Leech, 59
Lemon, 35, 40
_Lepidosaphes ulmi_, 37
_Lepisma saccharina_, 26
Lettuce, 55
_Leucaspis cordylinidis_, 38
_Leucaspis stricta_, 38
Leucojum, 66
Life-cycle of insects, 22
Lime-sulphur, 76
Loganberry, 41
Long-horned beetles, 64
Long-tailed mealy-bug, 34
Lupins, 52
_Macrosiphum rosæ_, 47
Magpie-moth, 24, 55
Management of garden, 74
Manure, 74
Mealy-bugs, 29, 30, 32, 34
Mealy-wings, 43
_Mecyna maorialis_, 52
_Merodon equestris_, 66
Metamorphosis, 24
_Micromus tasmaniæ_, 28, 34
Millepedes, 71
Mites, 67
Moulting, 22
Mouth appendages of insects, 19
Mulberry, 35, 36
Mussel scale of apple, 30, 37
Mustard, 44, 45, 48, 52
Myrtle, 36
_Myzus cerasi_, 44
Narcissus, 66, 68, 72
Narcissus flies, 66
Natural enemies, 77
Nectarine, 36, 44
Nervous systems of insects, 21
Nicotine-sulphate, 76
Northern Spy, 47
_Novius cardinalis_, 32
_Nyctemera annulata_, 24, 55
Oak, 37, 51
Oak-scale, 37
_Odontria zealandica_, 57, 64
_Oeceticus omnivorus_, 56
Oleander, 34, 35, 36, 40
Oleander-scale, 40
Olearia forsteri, 60
Olearia gall-midge, 60
Olive-scale, 30, 35
Onion, 66
Orange, 35, 40, 51
Orange-scale, 40
Orchids, 36, 40
_Orcus chalybæus_, 36, 40
Oviparous, 42
Ovipositor, 21
Palms, 34, 35, 36, 40
_Paratetranychus pilosus_, 67
Paris green, 76
_Paropsis dilatata_, 59
Parthenogenetic, 42
Passion vine, 34
Pastures, 64, 65
Peach, 35, 36, 38, 44, 48, 59
Peach-aphis, black, 44
Peach-aphis, green, 44
Pear, 34, 35, 36, 37, 38, 40, 41, 50, 59, 60, 61, 70
Pear and cherry saw-fly, 59
Pear and cherry slug, 59
Pear-leaf blister mite, 70
Pear-midge, 60
Pelargonium, 51
_Pemphigus populi-transversus_, 48
Pepper-tree, 35
_Perrisia pyri_, 60
Persimmon, 35
Phormium, 34
_Phthorimæa operculella_, 62
_Phylloxera vastatrix_, 46
_Pieris rapæ_, 55
Pine-tree chermes, 46
Plant food, 12
Plant-lice, 42
Plum, 34, 35, 36, 38, 40, 44, 48, 59
Plum-aphis, 48
_Plutella maculipennis_, 52
_Pontania proxima_, 60
Poplar, 35, 37, 38, 48, 64
Poplar Gall-aphis, 42, 48
Porina, 65
Potato, 34, 62, 72
Potato sickness, 72
Potato tuber-moth, 62
Predaceous wasps, 78
Privet, 38
Protozoa, 8, 15
_Pulvinaria camelicola_, 37
Pupa, 25
Puparium, 25
_Pyronota festiva_, 58
Quince, 38, 40, 41
Radish, 55
Ragwort, 24, 56
Rape, 45, 48
Raspberry, 36, 41, 67
Red currant, 44
Red oil, 76
Red orange-scale, 40
Red spider, 68
_Rhizoglyphus hyacinthi_, 68
Rhododendron, 47
_Rhophalosiphum nymphææ_, 48
_Rhophalosiphum persicæ_, 44
Root-knot eelworm of tomato, 73
Rose, 35, 38, 40, 41, 47, 51, 58, 67
Rose-aphis, 42, 47
Rotation of crops, 75
Round-headed borers, 64
_Saissetia hemispherica_, 36
_Saissetia oleæ_, 35
San José scale, 32, 38
Scale insects, 29
Scylla, 66
Seasonal history of insects, 22
Seeds, damage to, 65, 66, 71
_Sesia tipuliformis_, 61
Shallot, 66
Shepherd’s purse, 44, 52
Silver-fish, 26
Slugs, 8, 71
Smaller narcissus fly, 66
Snails, 8, 71
Soil fumigation, 76
_Sphinx convolvuli_, 54
Sphinx moth, 54
Spiders, 8, 67
Sprays, 75
Springtails, 66
Spruce, 46
Steam sterilisation, 74
Steel-blue ladybird, 36, 40
Stomach poisons, 76
Strawberry, 64, 68
Subterranean grass caterpillars, 65
Sulphur smudge, 58, 65
Syrphids, 66
Tachinids, 78
_Tetranychus telarius_, 68
Thrips, 27, 48
Thrush, 35
Tobacco, 54, 73
Tomato, 47, 54, 62, 73
Tomato root-knot eelworm, 73
Tomato stem-borer, 62
Tortoise beetle, 59
_Tortrix postvittana_, 51
Tree-lucerne, 64
_Trialeurodes vaporariorum_, 48
Tui, 35
Tulip, 66, 68
Turnip, 45, 48
Turnip-fly, 57
Turtle-scale, 36
_Typhlocyba australis_, 48
Vallota, 66
Vegetable caterpillars, 65
_Venusia verriculata_, 56
Vertebrates, 7
Violet, 68
Viviparous, 42
Walnut, 35
Watercress, 46, 52
Water lilies, 48
Wattle, 32, 41
Wax-eye, 35
Weta, 17
White butterfly, 55
White-flies, 48
Willow, 35, 37, 38, 60, 68
Willow saw-fly, 60
Wings of insects, 20
Wireworms, 65
Wistaria, 34, 35, 36
Woodlice, 8, 70
Woolly-aphis, 42, 47
Woolly-bear, 24, 56
*** End of this LibraryBlog Digital Book "Garden Pests in New Zealand - A Popular Manual for Prictical Gardeners, Farmers and Schools" ***
Copyright 2023 LibraryBlog. All rights reserved.