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.

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.

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 1½lb. 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.