Agricultural zoology

The mouth-parts are modified into a sucking and piercing beak. Head small. Legs usually slender, with two- or three-jointed feet. Wings are absent in several species (e.g. bed bugs); in one section (e.g. fruit bugs) the fore wings are half of leathery, half of membranous texture (Fig. 107); in others, all four wings are membranous (winged plant lice), or the fore wings are somewhat harder than the hind wings (frog-hoppers). Incomplete metamorphosis (p. 89). None of agricultural importance except—

Family: Aphidæ (Plant Lice).

Long, five- to seven-jointed antennæ. Long thin legs, no power of springing. Sucking beak long and thin. In the same species there are both winged and wingless aphides, mostly the latter. In autumn, male and female specimens are found. After pairing, the latter lay their eggs, which are destined to live through the winter. The aphides hatched from these the following spring are all females, but are distinguished from those of the previous autumn by producing living young, which contain at the time of their birth the germs of a new generation. The number of young produced by a single female, and the number of generations appearing within the year, vary according to the species. There are species in which each female bears from eighty to one hundred young, and nine to sixteen generations succeed one another in the year. In autumn males and egg-laying females once more appear. As a rule the eggs live through the winter, but the insects themselves may also do this. I must add that there are constant differences within the boundaries of the same species according to the habitat, and especially in the species which regularly wander, either from one plant to another, or from the leaves to the roots. But since the species injurious to agriculture do not migrate in this way, nothing further need be said on the point. As aphides suck plant juices during the whole of their lives, and have enormous reproductive powers, they are very destructive. They suck from stems and leaves the juices which would otherwise be used by the plants themselves for growth or for the production of flowers and fruit, and bear young, which bore their beaks into the same part in the immediate neighbourhood of their mother, and quickly begin to multiply in their turn. In this way, colonies consisting of a hundred or more individuals are regularly formed (e.g. on peas, beans, roses). A plant part attacked in this way shrivels for want of nourishment, and the aphides upon it would die if they did not wander elsewhere. The third generation usually contains, not only wingless individuals, but also others which, after repeated moults, fly away and start a new colony in another plant. Since aphides have many enemies (starlings, sparrows, grasshopper warblers, etc., lady-birds and their larvæ, drone fly larvæ, lace fly larvæ), and are often killed in large numbers by wind and rain, it only occasionally happens, particularly in dry summers, that they entirely or largely destroy the plants they infest. They injure plants, not only by drawing away their nourishment, but also by the separation of a sugary sticky fluid from the anus. If the minute drops of this fluid fall from the upper parts of an infested plant to the lower (garden and field beans), or from the leaves of an infested tree to the plants growing at its foot, or, as sometimes happens, are carried by the wind to more distant plants, great damage may be caused. The fluid evaporates and leaves behind a shining sticky substance, which closes up the stomata of the leaves, and partially checks exchange of gases (assimilation and respiration). Particles of dust, sand, and smoke carried by the wind, and also the cast skins of the aphides, stick to the surface of the leaves and render exchange of gases still more difficult. The leaves develop brown dirty patches, and die off. Besides this, the spores of disease-producing fungi, carried by the wind, stick very easily to the places covered by the sweet fluid, and readily germinate in it. Aphides may thus be the indirect cause of several diseases (e.g. smut). These insects are destructive, therefore, to other plants than those infested by them. Remedies: Spraying with any one of the fluids destructive to them—soapy water; a decoction of quassia chips; tobacco water, not too concentrated; Nessler’s fluid (1½ ozs. soft soap, 2¼ ozs. tobacco mixture, 2 ozs. fusel alcohol, half a pint ordinary alcohol, diluted with rain water up to a quart: when used, mix with one-fifth the quantity of rain water); Koch’s fluid (2 lbs. soft soap dissolved in half a gallon of hot water; ½ lb. of quassia chips extracted for twelve hours in 5 quarts of rain water, and the fluid thus obtained boiled and filtered. It is then added to the soap water, and the whole brought up to 10 gallons by addition of rain water). Spraying with one of the above-named fluids must be renewed in a short time, so as to reach all the aphides wherever possible; if even a few remain untouched, there will soon be a large number again. A warm evening is best for the spraying. Infested plants can also be strewn with finely powdered substances, or these may be scattered over them by means of a small bellows. Since such substances should remain on as long as possible, they should be used after rain or early in the morning, when the dew is still on the leaves. Among powdered matters suitable for the purpose, the following may be named: gypsum, lime, tobacco, wood-ash, insect powder (prepared from the flower-heads of Persian species of chrysanthemum and from tansy heads). It must also be pointed out, that these remedies must be employed as soon as the insects begin to show themselves in considerable numbers; it is not desirable to delay till the infestation has made considerable headway, as it is then much more difficult to get a satisfactory result. In some cases, it is desirable to cut off and burn or otherwise destroy much infested parts, or those parts on which the insects first begin to multiply (e.g. early cutting off of the tips of the stems in field and garden beans).

The species of aphis which most commonly occur upon cultivated plants are:—The Bean Aphis (Aphis papaveris), ¹⁄₁₂ inch, black; on the tips of the stems of field and marsh beans, also on poppy, turnips, lettuce, and on several wild composites and umbellifers. The Pea Aphis (Aphis ulmariæ), ⅛ to ⅙ of an inch long; green; July to September on peas, chickling peas, and several wild leguminous plants; very destructive. The Corn Aphis (Aphis cerealis), ¹⁄₁₂ inch, green or reddish brown, also reddish brown with green abdomen; June to August on rye, barley, oats and several grasses; sucks the axis of the ears, and the flower-stalks; as the (black) eggs remain on the stubble during the winter, it is advisable to plough this deeply in immediately after harvest. The Oat Aphis (Aphis avenæ), ¹⁄₁₂ inch, dark green, speckled with white; on oats and barley, scarcely ever on the ears, but on the leaf-sheaths and the upper sides of the rolled-up leaves. The Hop Aphis (Aphis humuli), ¹⁄₁₂ inch, green; on the under side of the hop leaves, and, when very abundant, on the scales of the fruit. The Cabbage Aphis (Aphis brassicæ), ¹⁄₁₂ inch, dark green, speckled with grey; from May to September on all kinds of cabbage, and also on other crucifers.

Seventh Order: Physopoda (Bladder-footed Insects).

Very minute insects, possessing a characteristic jaw apparatus, with which they pierce the outer skin of leaves or the parts of flowers, and suck their juices. The four small wings have long fringes at their edges; the fore wings are tolerably hard. The ends of the feet do not possess claws, but small bladders or suckers. The metamorphosis is incomplete. In some years, one or other of the species may increase to a very large extent, and these minute insects then fly about in swarms, especially on very hot days; and they also wander about in large flocks. If they settle on the face or hands of human beings, they cause a disagreeable and persistent itching, as they continually walk about.

The Corn Thrips (Thrips cerealium), ¹⁄₁₂ inch. Dark brown to black. Male wingless. Female with small wings bending outwards at their tips (Fig. 109); fore wings horny, hind wings membranous. Larva orange yellow; head, prothorax, and tip of the abdomen, black. After the last moult it becomes yellowish white, and acquires scale-like wings. Hybernates in the adult condition; lays its eggs on various grasses, also on different grain-plants. The larvæ, and, later on, the perfect insects are found in large numbers sucking the ovaries of flowering corn (wheat, rye, barley); as a result of which the ears do not fully develop, but wither away. Remedy: Deep ploughing of the stubble, by which the hybernating individuals are destroyed.

The Elder Thrips (Thrips sambuci) lives in elder, and sometimes also multiplies in very young field beans, the leaves of which blacken and shrivel up in consequence.

The Flax Thrips (Thrips lini) often injures flax.

Eighth Order: Diptera (Flies).

Mouth-parts elongated, adapted for sucking or piercing. Fore wings developed, rarely absent. Hind wings absent, as such,—altered into club-like bodies (balancers or halteres) often covered with scales. Metamorphosis complete. Larvæ always legless; most have biting mouth-parts and no distinct head (maggots); the head-bearing dipterous larvæ possess similar mouth-parts. The last become obtectate pupæ (p. 93), while the headless larvæ become pupæ within the larval skin.

Family: Culicinæ (Gnats).

Slenderly built, with long, thin legs. An elongated piercing proboscis in the female. The male with feebly developed mouth-parts, and feather-like antennæ. Both sexes suck up water and plant juices, and the female blood as well; hence only the latter bites, especially at night. They hybernate in the adult condition in cellars, barns, etc. The female lays 250 to 300 eggs on any floating object in stagnant water (pools, ditches, water-vessels). The larvæ (with large head, well-developed prothorax, and a breathing-tube on the abdomen) live in water, as do the pupæ. Several generations annually; especially in damp summers and districts where the draining of the soil leaves much to be desired. Although sand flies torment our domestic animals more than gnats, yet these also may be very troublesome to them. They principally attack the less hairy parts of the body (inner side of the ears, nose, mouth, corners of the eye, arms, sexual parts). Remedies: Thorough draining of the soil. Washing the domestic animals to be protected with a vinegar extract of walnut leaves; rubbing with walnut leaves. Wherever possible, any sores should be covered up, as they attract gnats, sand flies, and flies; or the skin near them may be painted with turpentine or very dilute carbolic acid. This is the less to be neglected, as several kinds of flies eagerly lay their eggs in the sores of domestic animals.

Family: Gallicolæ (Gall Gnats).

Small gnats with large broad wings, much narrowed at the root, rounded at the tip, and generally rough with hairs. Feelers made up of a large number of spherical or cylindrical joints, covered with spreading hairs. Proboscis short, legs long. The female has an ovipositor, with which she inserts eggs in any part of a plant. At this particular spot a luxuriant growth of vegetable tissue takes place later on, of varying extent, and even forming a regular gall. The species of gall gnat are usually brightly coloured, often red or yellow; these colours are lost, however, in dried specimens. The larvæ are spindle-shaped, yellowish white, yellow, or red; they become pupæ either in the soil or within the part of the plant which they inhabit. Several species are destructive to fruit-tree culture or forestry; I mention here only the most destructive kinds which attack cultivated plants.

The Hessian Fly (Cecidomyia destructor).

Female about one-eighth of an inch long, male somewhat smaller. The former velvety black, with black hairs, red belly, and red markings; wings greyish; antennæ one-third the length of the body. Male black, with reddish-yellow hairs, dirty red belly, and red markings. The name “Hessian flies” was given in North America, during last century, because it was believed they were introduced from Germany, in 1778, by Hessian soldiers, in their straw. It is still very destructive in North America, also in Germany, Russia, England, and Scotland. Habits: During April or May, on warm still evenings, the female lays her eighty or ninety eggs, singly or in pairs, on the lowest leaves of the still very short haulms of rye, wheat, and barley. Eight days, on an average, after this the maggots, which are at first oblong and spotted with reddish yellow, are hatched, and glide down into the leaf-sheath, where they begin to suck the haulm. They gradually alter their shape, becoming ovoid, and transparent with the exception of the large yellowish white, quite opaque fat body. They soon become pupæ (Fig. 111), which look like grains of linseed, and are found in summer on the haulms of the ripe grain. The presence of the constantly sucking larvæ causes great and injurious distortions of the plant, especially obvious during the flowering time, and for a short time afterwards. The haulm withers, and shrivels at the point where the larvæ are present, i.e. above the lowest node, or the lowest but one. At the time when the haulm begins to turn yellow—that is, when the grain begins to ripen,—the larvæ become pupæ; the haulm now easily breaks off at the infected spot; a strong wind or heavy rain throws it to the ground. A badly infested field looks, on this account, as if a herd of cattle had got loose and trodden it all down, or as if the grain had been devastated by hail. Only a few haulms bear ears containing normally developed grains. The flies emerge from the pupæ in August and September, after which the females quickly seek the winter corn, and lay their eggs singly or in pairs on the leaves of the yet young plants. The larvæ creep between the leaf-sheath and the still quite undeveloped haulm, and, in the case of small haulms, a number of larvæ may collect together in the immediate neighbourhood of the root, causing a spherical swelling. In many cases the plant dies if its lower parts are inhabited by many larvæ. Before winter, the larvæ attain their full size, leave the plants, and creep into the soil, where, in the following spring, they become pupæ, from which flies emerge fourteen days later. There are, therefore, two generations annually. The spreading of Hessian flies into regions where they were formerly unknown may be caused by (a) straw containing the linseed-like pupæ (straw for paper manufacture, packing, etc.); (b) grain, among which are often found pupæ that have fallen out of the haulms among the separated grain. Remedies: 1. Sowing the winter grain as late as possible, so that the females of the summer generation when they come out of the pupæ will find no winter-grain-plants in which to lay their eggs. 2. Ploughing up the stubble immediately after harvest, or else burning it, so that the pupæ found above the lower nodes are either deeply buried or else burnt.

The Scarlet Wheat Midge (Cecidomyia equestris).

Female about ⅛ inch, male ¹⁄₁₂ inch; cherry red, with yellow hairs; back of the thorax dark brown. Antennæ as long as the body in the male, half as long in the female. On the wing from May till June; lays its eggs on the leaves of grain-plants, at the base of the uppermost leaf by preference. The blood-red maggots, when they are hatched, let themselves slide down, and get between the leaf-sheath and haulm. Here they work themselves into the haulm, making a longitudinal groove, the walls of which swell more or less, and the end of which is indicated by an obvious transverse thickening. The leaf-sheath hiding the attacked part of the stem is usually more or less swollen. These gall-like outgrowths take up a great deal of nutritious matter, not only from the affected haulm but also from the plant at large, so that the regions not directly attacked are retarded in their growth. The larvæ are full-grown at harvest time, leave their hiding-places, and let themselves fall to the ground, where the following spring they become pupæ, from which midges quickly emerge. Remedy: After a year in which the insect has caused great damage, the fields must be deeply ploughed in order to kill the larvæ, which would otherwise live through the winter.

The Wheat Midge (Cecidomyia tritici).

Male ¹⁄₂₅ inch, female (Fig. 110) ¹⁄₁₇ inch, and possessing an ovipositor which, when extended, is twice that length. Citron yellow, slightly hairy; antennæ blackish, eyes black, legs dirty yellow. In spring or early summer, the midges creep out of the soil in fields where wheat has been planted the previous year. After pairing, the females wander to fields where wheat or, more rarely, rye is growing. The attacks of the midges commence when the ears begin to emerge from the leaf-sheaths, and are continued throughout the flowering time of the wheat. At night the female pierces the glumes with her ovipositor, and lays three to ten perfectly transparent eggs in each flower. Each midge lays eggs in several flowers, but two or more midges may use the same flower for this purpose, so that as many as thirty maggots may be found in one bloom (Fig. 112). The maggots, which are hatched out in a week, creep down to the ovary and suck its juices. If many maggots live in one flower it is sure to die, but if there are only a few it may produce a grain, though this may be small. Ears infested by the maggots develop yellow spots later on; many ears remain quite empty, and consequently thin and upright. Full-grown maggot: ⅛ inch; straw yellow to chrome yellow; quite transparent when very young. Is fully developed in three weeks, and then lets itself fall to the ground (July or August). Becomes a pupa the following spring; fourteen days later the midge escapes.

Family: Rostratæ (Crane Flies, Daddy Longlegs).

These very long-legged gnats live on the juices of plants, and do not sting. The larvæ are legless, without a hard well-marked head; those of most species live in mouldering plant parts (e.g. rotten wood), or the decaying manures of our fields and meadows. A few species, however, are very destructive, since they injure roots and other parts of cultivated plants. The adult and larval stages of all the injurious kinds are not yet distinguished. We know that the larvæ of the yellow and spotted Tipula maculosa are chiefly destructive in sandy soil; while more binding clay soil and rich garden earth are infested by the larvæ of Tipula oleracea (Fig. 113), and damp meadows by those of Tipula paludosa. The two last-named species are very much like one another; grey or greyish brown with bright brown wings, having dark front margin. Much is still unknown about the habits of “crane flies”; my researches relate to the Yellow-spotted Crane Fly (Tipula maculosa). The adults fly about in swarms during summer, usually from the beginning of June, in the fields where the larvæ lived in spring. They lay their eggs either in the same fields or (usually) in others, and are blown about for long distances by the wind. Where the flies settle they lay each time two or three black ovoid eggs, bent like a sickle, and repeat this till all the eggs (200 to 250) are laid. Those fields which have previously been grass land are the most infested by the crane flies. The larvæ are headless, grey to lead coloured, with small prickles at the hinder end of the body, and they first appear, in large numbers, under the pieces of turf which are left behind in such fields, and which appear to be the centres from which the destruction of the standing corn begins. The larvæ are hatched out in summer, during the later part of which, and during autumn, they devour plant roots; after hybernating, they again attack the underground parts of plants the following spring. They devour most readily the roots of grass and corn, but also those of clover, rape, and several other plants, including some found in flower and kitchen gardens. They are mainly injurious either in autumn or spring, according to the nature of the plants attacked. Young grain-plants are killed by them, older ones usually not. On fields where winter corn grows they therefore do most damage in autumn, while this is the case in spring on land where summer corn is cultivated. They are sometimes harmless, since they can also feed on roots left behind in the ground. The larva do not limit their ravages to underground parts; in the evening, and also in the daytime during dark damp weather, they devour parts of the first leaves of very young corn plants, though the damage thus effected is often inconsiderable. In May the larva is ready to pass into the pupa stage; it comes near the surface and becomes a brown pupa, bearing small spines on the abdominal rings. After a rest of fourteen to seventeen days, the pupa works its way upward till the front part of its body sticks out of the soil. The fly then escapes. Enemies: Mole, shrews, wagtails, grasshopper warbler, rook, gulls. Remedies: When the maggots are very destructive in gardens they may be collected, preferably in wet weather, since they then leave the soil during the day. If they appear to an injurious extent on summer corn, the fields should be rolled in April (either with the ordinary or the spiked roller). At the time (June) when the crane flies swarm about the fields and meadows in flocks, thousands of individuals can easily be caught with a net.

Gnats with relatively short legs, and antennæ which are in any case shorter than the body, and are usually quite short and cylindrical, possessing, however, six or more joints, while the antennæ of true flies usually have only three joints. The gnat flies form, as it were, the transition between the slender gnats with their long legs and antennæ, and the more thick-set flies, the legs and antennæ of which are short. Here belong the genera of Shade Gnats (Sciara, e.g. Sciara Thomæ, the larvæ of which often wander about in companies, as the so-called Army Worm), the Sand Flies (Simulia), and the Hair Gnats (Bibio, e.g. the Garden Hair Gnat, Bibio hortulanus, the larva of which gnaws the roots of plants, especially in humous garden soil).

The Sand Flies, or Mosquitoes (Simulia),

have thick-set bodies, short legs, and short nine or ten-jointed antennæ; they are from ¹⁄₂₅ to ⅕ of an inch long, and have a short but sharp proboscis, with which they suck up the flower juices which constitute their chief food. But the female also sucks the blood of human beings and animals, making herself exceedingly annoying in this way. Its larval state is passed through in stagnant water; its appearance is therefore local, and is especially favoured by damp summers. The mature sand flies are found from early spring or through the whole summer; several generations succeed one another in the same year. Sand flies often appear in swarms, containing thousands of individuals. Since the female eagerly creeps into the ears, noses, and corners of the eyes in horses and oxen, she is extremely annoying and even dangerous. Her bite produces a smarting sensation, and may cause actual boils to form in the skin. When a large swarm of sand flies settles on a herd of cattle or on some horses, these animals become maddened and furious; they often rush wildly round for so long that they fall down dead. Simulia reptans is a common British form. Remedies: Compare what is said on p. 165, about gnats. Sand flies can usually be kept from horses’ ears by means of ear-caps.

Family: Tabanidæ (Gad Flies).

Large or medium-sized flies with thick-set body, large broad head, flat abdomen, and strong legs. The proboscis is less developed in the male, which lives merely on plant juices, than in the blood-sucking female. The cylindrical whitish larvæ live in earth, and are harmless. But the female insects bite human beings, and the larger kind attack horses and cattle in such a manner that blood-drops may be seen on the ground under the animals attacked, if these remain for a time in the same spot. There belong to this family: 1. The Breeze Flies (Tabanus), large insects up to ⅘ inch long, which are seen flying about with a buzzing sound over meadows and fields in the sunshine (Ox Fly = T. bovinus; Horse Fly = T. autumnalis). 2. The Lesser Breeze Flies (Hæmatopota), smaller and more slender, with grey wings, bite most before a storm and in hot sultry days. 3. The Blinding Breeze Flies (Chrysops), as large as the Lesser Breeze Flies, but broader, with shining golden-green eyes and wings marked with black. Remedies: Compare p. 165, and above; draining the soil, however, is no good here.

These are flies with three-jointed antennæ, constructed on the type seen in the common house fly. Here are included the Caterpillar Flies (Tachina), the Flesh Flies (Sarcophaga), Common Flies (Musca), Flower Flies (Anthomyia), Green-eyed Flies (Chlorops), etc.

The Caterpillar Flies (Tachina)

are black, grey, or reddish yellow flies, reminding one by their appearance of the common house fly or the blue-bottle. They play the same part in the economy of nature as the sand wasps (p. 129), but always lay their eggs externally on the skin of the host; the maggots consequently never prey on those insect larvæ which live in the tissues of plants or in the soil.

The Flesh Flies (Sarcophaga)

have a longish abdomen, with large bristles on the hinder margins of the segments. Thorax with three longitudinal streaks. The flies suck up sweat, but do not bite. The eggs develop within the abdomen of the mother; the flies lay the young larvæ in dead flesh; also, if not kept clean, in wounds of human beings and animals,—sometimes, too, in the genital opening of horses, cattle, and swine, in which case the maggots live as true parasites in the vagina and uterus, causing a secretion of mucus, upon which they live. Two to three generations yearly; fifty to eighty maggots each time. Remedies: On keeping the flies from cattle, cf. p. 165; to keep them from meat, flynets, a gauze cover. Blow Fly (S. carnaria), with black speckled abdomen.

are coloured dark or shining green. The headless white maggots live in dung (House Fly = Musca domestica), in fresh or decaying meat (Blue-bottle = M. vomitoria), exceptionally (M. vomitoria) in wounds that are not kept clean, or in the vagina of several domestic animals. Remedy: Compare above (“Flesh Fly”).

The Flower Flies (Anthomyia).

These are found on flowers, and resemble many common flies in appearance and colour. The headless white maggots live in dung, also in decaying or sound parts of plants; a few species may sometimes develop in the one kind of material, sometimes in the other. Anthomyia meteorica swarms round the heads of domestic animals, and may even cause inflammation of the eyes and ears. The Wheat Bulb Fly (Anthomyia coarctata, about a quarter of an inch long, yellowish grey, with black hairs) lives as a larva during winter and spring in the hearts of rye and wheat plants, the leaves of which become yellow in consequence. During April and the beginning of May the larvæ quit these plants and become pupæ in the ground. The second generation can, in like manner, live in various kinds of summer grain. The Lupine Fly (A. funesta)—nearly one-fifth of an inch long, brownish grey (male) or whitish grey (female), with black legs—digs, when a larva, tunnels in the roots, stems, and seed-leaves of young lupine plants, causing the root and stem to turn black, and the seed-leaves to wither. Preventive Measure: Early sowing of the lupines. The Mangold and Beet Fly (A. betæ), a quarter of an inch long, yellowish grey, lays its eggs, five to eight in number, in the young leaves of mangold and beet. The maggots devour the green substance of the leaf between the two layers of epidermis, so that the leaves die. In June the maggots creep out of the leaves, and become pupæ in the soil. The flies quickly escape, and two or three generations follow one another in the year. As, however, the leaves are now larger, the later generations only effect a small amount of damage. Preventive Measure: Close sowing of the turnips, so that even if many are killed there will still be enough young plants. The Cabbage Root-eating Fly (A. radicum) and the Radish Fly (A. floralis) live as fleshy, wrinkled, dirty white maggots with black dots, in the underground parts of turnip, cabbage, horseradish, radishes, etc. They lead a similar life to the Cabbage Fly (A. brassicæ), the cylindrical, smooth, yellowish white maggot of which lives in the underground parts of cabbage, turnip, and rape. The roots attacked swell here and there (Fig. 116), and later on decay; the leaves of the infested plants first become of a dull leaden colour and then wither. Entire fields of cabbage, rape, or turnips, are often destroyed by cabbage fly maggots. The insect passes the winter in the pupa state; the flies appear early in the spring, and usually twice more later on. It is therefore most desirable to pull up and burn the infested plants as soon as possible. A proper rotation of crops should also be practised. [The Onion Fly (A. ceparum) maggot feeds within the bulbs of stored onions. The male fly is grey, the female yellow.]

one-fifth of an inch long, slender, with a metallic sheen, almost hairless, black, with dirty yellow legs and wings of glassy clearness. These small flies abound in front of the windows of places where cheese is stored; in summer and autumn the shining white maggots, which are cylindrical in form with tapering ends, and one-third of an inch long, live in large numbers in old cheese, gnawing it through and through, and making it dirty. Now and then they spring forwards by bending their bodies into a circle and suddenly straightening them again. They become pupæ on the walls or in straw, near the cheeses from which they have crept out. Remedies: Keeping the cheeses clean; mechanical exclusion (gauze screens outside the windows, enclosure in chests).

The Green-eyed Flies (Chlorops)

include a number of small flies, under one-sixth of an inch long, with spherical head, rounded greenish eyes, strongly arched thorax, and short egg-shaped abdomen, pointed in the male and blunt in the female. The headless larvæ live in the haulms of grasses and species of grain; the life history of a few forms only is adequately known. A few are harmful, especially as there are two or three generations annually. The late summer generation often appears in large numbers, indeed in actual swarms. Since no species lives exclusively on corn, it is impossible to keep them down for a long period of time. I describe only two species:—

The Ribbon-footed Corn Fly or Yellow Haulm Fly (Chlorops tæniopus), nearly one-sixth of an inch long, shining yellow; the antennæ are black, and there are three longitudinal stripes on the dorsal side of the thorax and four transverse bands on the abdomen of the same colour; the latter region is scarcely longer than the thorax. The insect (Fig. 117) is on the wing in cornfields about the middle of May. It lays its eggs separately on the upper leaves of various species of wheat, rye, and barley, choosing the upper side of the blade, not far from the sheath. Only those plants are selected for the purpose in which the ears are still hidden deep down between the leaf-sheaths. Wheat plants are picked out whenever possible. The maggot when hatched works its way between leaf-sheath and haulm, digging into the latter. It is yellowish white, clear and translucent, and about a quarter of an inch long. While still young it penetrates the haulm, and then attacks the developing ear or the upper part of the haulm which immediately adjoins this, and travels gradually up to the first node of the haulm or nearly so, always continuing to slowly suck. Thus a furrow, from 2½ to 3½ inches long (Fig. 118, C and D), is formed along the surface of the upper part of the haulm, and often also along the lower part of the ear. The part of the haulm attacked swells transversely, and the part below often remains short, so that the ear cannot emerge from the leaf-sheath; but, in any case, only small worthless grains are developed. The furrow is always much deeper below than above, and its margins thicken in consequence of the swelling of the tissues of the haulm. At the end of June or in July, the larva becomes a pupa at the lower end of the furrow. The yellowish-brown pupa (Fig. 118, B), one-fifth of an inch long, remains as such in the furrow for three weeks; the fly emerges in August. Very considerable damage may be done by the first generation, of which the habits have just been described. During 1869 in Silesia, from two-thirds to five-sixths of the ears in many fields remained hidden in the leaf-sheaths, and consequently gave no increase. The first generation of the ribbon-footed corn fly can also develop in the way described in the haulms of several grasses, e.g. in species of Poa and Holcus.

The flies, emerging in late summer, lay their eggs, here, too, separately, on the leaves of grass or corn. Wherever possible, they seek out for the purpose the winter wheat plants then present in the fields, but also content themselves with rye, or even with wild or meadow grasses; they have to be satisfied with grasses if, at the time of egg-laying, the winter corn is not yet up. The maggot, when hatched, works its way to the inner side of the leaf-sheath, and thence to the apex of the still very small haulm; there it remains during the winter. The damage becomes apparent the following spring. The growth in length of the haulm in question is extremely small, while growth in thickness increases to an abnormal extent. Almost all the leaves completely surround the haulm, which swells to an enormous extent (Fig. 119), together with the enclosing leaf-sheaths, which are much broader than usual. The unattacked plants are naturally much larger than the sickly ones, and deprive these of air and light, so that they die down, being overshadowed, not only by the sound haulms, but also by their own secondary shoots. The resulting damage may be tolerably great, especially at the edges of the field. It may happen that both summer and winter generations of the ribbon-footed corn fly are harmful in the same district; but it frequently happens that only one or the other is complained of in a particular spot. It is only natural that the flies, which swarm around in May, and again in August, September, or October, should not always find suitable corn plants upon which to deposit their eggs. In such cases grasses are used. Remedies: Sowing the summer corn as early as possible, that it may be developed to a stage which is unsuitable for the purpose of egg-laying, before the flies appear. The winter seed, however, must be sown as late as possible, so that the second generation of flies may find no corn plants fit to lay their eggs upon. Bearded wheat, especially the strongest varieties, should be sown in preference to awnless wheat. Careful tillage and suitable manuring, so that strong plants of rapid growth may be produced.

(Fig. 120, C) is about one-tenth of an inch long, shining black, with a metallic sheen. Legs short, feet yellow. Maggot (Fig. 120, A) yellowish white, about one-eighth of an inch long, cylindrical, and tapering in front. Usually three generations. 1. The maggots of the first generation are found during May, in the lower part of the haulm of summer corn (especially oats and barley); the plants attacked either die off entirely, or some haulms develop further, remaining small, however, and yielding only a few light grains. The base of the haulm thickens abnormally, but the growth in length is always small; the leaves, too, grow badly, first becoming yellowish at the tip, and then entirely yellow or reddish. The symptoms of disease are exhibited to a less or greater extent, according as few or many (even up to ten) maggots inhabit the base of a plant. The shining brown pupæ (Fig. 120, B) are found in the lower part of the haulm, or between the leaf-sheath and the haulm (Fig. 120, D). The adult insect is on the wing at the end of May and in June. The first generation often appear on wild or meadow grasses, and are chiefly seen on summer corn when this is sown late or develops slowly. 2. The maggots of the second generation are found in average cases during July, on the as yet scarcely ripe grains of late summer corn, principally those of oats and barley, often occurring also in the haulms of grasses. They keep between the awns, and suck the juices of the soft developing grains, which are rendered incapable of growth, and in any case remain light. The maggots of the second generation develop more quickly than those of the first or third; they are mature in three weeks. The pupa rest is very short, and the flies appear in August, September, or October. They lay their eggs on the leaves of winter corn or winter grasses, and from these eggs are developed (3) the maggots of the third generation, which are to be found, during September and October, in the heart of winter corn and grasses, injuring these plants in exactly the same way that the maggots of the first generation injure the summer corn. The insect passes the winter as a pupa in winter corn plants or grasses. It is but very rarely that all three generations infest the corn of any particular region; as a rule, only the first, second, or third generations do this, or the first and third; in such cases the other generations live on grasses. Remedies: Extermination of the insect is impossible, since it can always go from corn to grass plants. Oats and barley are almost always attacked in spring, if in the immediate neighbourhood there is winter rye inhabited by the maggots, for the flies, when they emerge the next spring, seek out the summer corn. This may, however, be made impossible, or at least difficult, if a field of peas, clover, lupines, rape, or some other crop not of gramineous nature, is interposed between fields of winter corn and those of oats, barley, or similar late sown crops of summer corn. Sowing the summer corn (especially oats and barley) as early as possible.