Part 19

Moth (Fig. 105): Length ⅜ inch; span of wings about ⅖ inch. Fore wings fawn-coloured, with metallic sheen; alternating short, white, and dark lines on the front margin. Hind wings black, with bronze sheen and white fringe. Caterpillar: ⅓ inch long; 16-legged; pale green, with brown or black head, neck-shield, and last body segment. The thoracic legs are black. Dark warts on each segment. Habits: Compare the succeeding species.

FIG. 105.—The Fawn-coloured Pea Moth (Grapholitha nebritana). ]

The =Crescent Pea Moth= (Grapholitha dorsana).

Moth: Somewhat larger than the preceding species. Fore wings olive brown, with many small short white lines on the front margin. A yellowish white crescent on the middle of the hinder margin. Hind wings brownish. Caterpillar: Nearly ⅖ inch long, 16-legged, orange yellow, with brown or black head, neck-shield, last body segment, and thoracic feet. Covered with brownish-yellow warts. Habits: The moths fly about in large numbers round the pea blossoms, always a short time after sunset. The female lays one, two, or at most three eggs, on a very young pod, or on an ovary. In fourteen days the caterpillar is hatched, bores into the pod, and attacks the peas. The opening made in the margin of the pod closes up again. The pod generally ripens early. When it opens, the full-grown caterpillars creep out, and become pupæ in the soil, within a web, where the pupa lives through the winter. The peas attacked are always covered, while in the pod, with the coarse-grained excrement of the caterpillars, and are often united two or three together by web fibres. Remedy: Deep digging of the soil before the winter, or, still better, deep hoeing as soon as the pea crop is gathered in. In this way many of the caterpillars or pupæ hidden in the soil will be destroyed.

Family: =Tineidæ= (Leaf-miners).

FIG. 106.—The Larch Moth (Coleophora laricella). ]

These moths are the smallest of the Lepidoptera. Like the snout moths, they have strongly developed labial palps, but are distinguished from them by their small wings; the hind wings are especially small, and have sharp tips. The extent of the wings is increased by a broad marginal fringe. When at rest, the wings slope like a roof, and the fringe near their tips is often turned upwards. Antennæ thread-like, tolerably long—in the males of a few species may even be very long. Caterpillars slightly hairy, with five, or, rarely, four pairs of pro-legs. To this family belong the well-known =Clothes Moth=; the =Corn Moth=, living in stored-up grain; and also—

The =Carrot Moth= (Depressaria nervosa = Hæmylis daucella).

Moth: Length ⅖ inch. Span of wings rather over ⅘ inch. Fore wings reddish-grey brown, blackish on the nerves, and with scattered whitish markings. Hind wings more of a grey brown. Thorax and abdomen very shiny, and somewhat brighter than the wings. Caterpillar: Nearly ⅖ inch long, tolerably thick, especially in the middle, and variegated. Head, thorax, and last body segment shining black, the last two regions with reddish-yellow margin, and the thorax, in addition to this, divided into right and left halves by a longitudinal yellow line. The rest of the body is olive green; a broad orange-coloured line divides it into a darker dorsal and a lighter ventral side. On the back many ill-defined warts of a shining black colour. Habits: In March and April many of the carrot moths which have survived the winter come out of their hiding-places; they only fly at night. The eggs are laid separately on umbelliferous weeds, carraway, or carrot plants. The caterpillars are first seen when the plants flower; they live on the flower-stalks, which they bind together by a few threads, and devour the flowers and young fruits, sometimes even the flower-stalks. The caterpillars are very active, and let themselves down by a thread when disturbed. Usually they are fully grown in five weeks, and then bore into the stalks of the plant, where they become pupæ. It is not known whether there are one or two generations. The caterpillars are found at very various times, from May to August.

The =Diamond-back Moth= (Plutella cruciferarum = Tinea xylostella).

Moth: About ¼ inch long; span of wings ⅗ inch. Fore wings small, lancet-shaped, with long fringes. Ground colour yellowish brown, darkly speckled. Hind wings brownish grey, small, strongly fringed. When at rest the long fringes form a sharp backward and upwardly directed comb, while the antennæ are applied together and stretched straight forwards. Caterpillar: About ¼ inch long, tapering in front and behind. A beautiful green, with a black head. Lives hidden under a very thin web or under a few fibres, on the lower side of the leaves of cabbage, rape, and other crucifers. Habits: The pupa lives through the winter; the moths emerge in May, and fly about in the evening. Two generations; the first generation of caterpillars in the first half of July, the second in late summer. The second generation is particularly apt to be destructive to cabbage. Pupæ found on the leaves of the plants attacked, and surrounded by a thick web.

SIXTH ORDER: Hemiptera (HALF-WINGED INSECTS).

FIG. 107.—Left pair of wings of a Bug. ]

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).

FIG. 108.—The Bean Aphis (Aphis papaveris); a larva of the same below. ]

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.

FIG. 109.—Corn Thrips (Thrips cerealium). ]

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.