Part 9
The =Gall Weevils= (_Ceutorhynchus_) are very small beetles with thick-set bodies. In a state of rest the proboscis is folded back into a ventral furrow, situated between the fore-hips. They are black, and thickly covered with grey hairs. Live on cruciferous plants. The =Turnip Gall Weevil= (_Ceutorhynchus sulcicollis_), one-eighth of an inch long, dull black, with many grey hairs on the ventral side and few on the dorsal side. The deeply pitted neck-shield has in its centre a well-marked longitudinal furrow. Wing-covers deeply furrowed. The beetle appears in April, and gnaws the flowers and shoots, but can scarcely be considered as harmful. In late summer or autumn, after the sprouting of the winter rape, the female bites into the root immediately under the surface of the soil, or into the lower parts of the stem, so as to form a hole in which she lays one or two eggs. As the larva begins to develop, the surrounding parts of the stem or root grow into a gall-like swelling (Fig. 80). At the beginning of spring the developed larvæ creep out, and become pupæ in the soil; in April the beetle appears. If the Ceutorhynchus galls are only present in small numbers they damage the rape plants only to a small extent, but when ten to twelve are found in one plant the roots grow crooked, and remain short, and consequently the growth of the overground parts is detrimentally affected. Ceutorhynchus galls are found, not only on rape, but also on the different kinds of cabbage, and on turnip plants. In the last case they often occur in such numbers that the turnips do not develop at all, and the overground parts also remain small. There is a similar form (_C. assimilis_), as large as the preceding species, but somewhat slimmer, and, on account of greater hairiness, greyer. Appears in spring on flowering rape and several kinds of cabbage, as well as on similar cruciferous plants. It is harmful because the beetles gnaw the buds and flowers, and the larvæ feed on the seeds within the pods. The attacked pods ripen early, and open so that the larvæ fall to the ground, where they become pupæ. Usually only a single larva is found in each pod. The =Rape Gall Weevil= (_C. napi_), somewhat larger than the two preceding species, has a neck-shield which projects strongly forward like a collar, and is marked by a median longitudinal furrow. It is covered with yellowish-grey hairs. At the time when rape blooms it appears upon the flowers. The female lays her eggs singly in a hole previously bored in the stalk by her proboscis; during spring and early summer the larva eats out the stem, which turns brown inside, and becomes diseased or even dies.
Family: =Chrysomelidæ= (_Leaf Beetles_).
Small, generally thick-set beetles, arched on the upper side, with eleven-jointed antennæ thickening somewhat towards their tips, and four-jointed feet. The first joints of the feet are covered with felt-like hairs on their under sides (Fig. 81). The larvæ have three pairs of thoracic feet, and, in addition to this, there are in most species a pair of caudal pro-legs. Live in the inside parts of plants (stems, leaves), and are usually elongated and yellowish white; those which live on the outside of plants are more convex, shorter, and thicker, more or less hairy, often of a striking colour, and always with dark spots. The beetles eat leaves; the larvæ feed upon parts of the same plants, sometimes living outside upon the leaves, or it may be excavating channels in the inside of a leaf or of the stem. Most leaf beetles lay many eggs, and in many species there are several generations annually. The plants attacked by them are often stripped quite bare. Here belongs the blue =Alder Leaf Beetle= (_Galeruca alni_), the =Poplar Beetles= (_Chrysomeli populi_ and _C. tremulæ_), the =Asparagus Beetles= (_Crioceris merdigera_ and _C. duodecimpunctata_), etc. Of species injurious agriculturally, I will first mention the =Colorado= or =Potato Beetle= (_Chrysomela decemlineata_). This beetle originally lived in the west of the United States on wild solanaceous plants; but as soon as potato culture extended to the west the beetles also attacked potato plants. As soon as the insects had spread to this plant they began to appear in great numbers owing to their very great powers of reproduction; and they quickly spread from one field to another, always going further and further east. 1859 was the first year when they became notorious as pests, and, since they first appeared as such in the State of Colorado, the insect received the name “Colorado Beetle.” In a short time the beetles spread to the east, especially to places where potato culture was carried on; in 1865 they crossed the Mississippi, and in 1870 they were already spread over the states of Indiana, Ohio, Pennsylvania, Massachusetts, and New York. They were soon found in all the eastern states, and European farmers began to be alarmed. In most of the countries of Europe police regulations were made for the purpose of preventing the introduction of the unbidden guests. Colorado beetles have indeed been brought several times to Germany on board ship, but in almost all cases the pests so introduced have been recognized and caught. Twice during 1877 they were able to increase (Mulheim, Schildau), and the same thing has happened once at a more recent date (Torgau); but the vigorous action of the authorities quickly exterminated the beetles.
Beetle (Fig. 81), half an inch long, dusky yellow, with five longitudinal black streaks on each wing-cover, and black markings on the neck-shield. Larva (Fig. 82), half an inch long, thick, fleshy; legs short and weak. Orange-yellow, with shining black head, and with black spots on the body segments. The younger larvæ are darker, almost blood red. When the young potato plants come up, the beetles which have survived the winter creep out of the soil and devour the margins of the young leaves. The female lays her yellow eggs (700 to 1200?) in heaps on the leaves (Fig. 82, _a_). After a week the larvæ appear, and carry on the work of the beetles. They attain their full development in seventeen to twenty days, become pupæ in the soil, and the beetles of the second generation make their appearance in the middle of June. Still a third generation may appear the same year. Since a considerable time elapses between the laying of the first and second batches of eggs, one usually sees eggs, larvæ, pupæ, and beetles at the same time. Entire potato fields are eaten bare by the beetles and their larvæ, the formation of the potatoes being quite prevented. _Remedies_: Energetic measures must be taken on the first appearance of the beetle in any district. Where possible, all the beetles and larvæ must be collected, the plants being dug up and destroyed with the beetles, pupæ, larvæ, and eggs adhering to them. Petroleum must then be poured over the whole field and set on fire, so as to destroy any insects which may be hidden in the soil. Spraying the attacked plants with Schweinfurt green.
The =Cloudy Tortoise Beetle= (_Cassida nebulosa_)—Fig. 83. One-fifth to one-fourth of an inch long; the broad neck-shield projects in front over the small head. The wing-covers, too, are much broader than the body of the animal; they are longitudinally ribbed. Dorsal side reddish brown, in young individuals greenish; always with black spots. Ventral side black. Larva elongated oval, yellowish green. Segments of the body beset with thorn-like structures bearing lateral branches; the last segment possesses a “tail-fork,” which the larva usually carries bent over its back and on which it heaps up its dung. The beetles which have survived the winter usually attack in spring only wild goose-foot and orach plants, on which they lay their eggs in heaps. The larvæ quickly appear, and to begin with chiefly keep to the under sides of the leaves. They are sluggish, grow quickly, and devour the leaf substance; when fully developed they cement themselves to a leaf and become pupæ. In June the beetles of the second generation appear, which again lay their eggs on the leaves. In favourable weather there may be even a third generation. In many it happens that the beetles of the second generation migrate to beet or mangold plants, sometimes damaging them to a very great extent. _Remedy_: Rooting out species of goose-foot or orach.
The =Earth Fleas=, or =Flea Beetles=, are all small leaf beetles with the power of springing, and therefore provided with thick thighs. Here belong:—
The =Rape Flea Beetle= (_Psylliodes chrysocephalus_)—Fig. 84. Egg-shaped. Hind feet not inserted at the ends of the shanks, but higher up. The first joint of the foot is as long as the others put together. The rest of the hind foot is bent in a knee-like way on the first long joint. Shining blackish brown or blackish green, rarely brownish. Larva one-fifth to one-fourth of an inch, dusky white; head, neck-shield, and last segment of the body blackish brown. In spring and during the entire summer the beetles are found upon the plants of winter rape. Although they gnaw the leaves and the immature shoot the damage caused is small. In late summer or autumn the female beetles lay their eggs separately at the bases of the leaf-stalks of the young winter rape plants. The larvæ which emerge bore into the leaf-stalk, and eat it completely out during autumn, winter, and spring, so that the leaf dies. Since the eggs are laid separately the larvæ do not all develop at the same time in the spring. In spring many larvæ eat their way from the leaf-stalks into the still very short stem, which consequently ceases to develop. It often happens that most, or even all, of the plants in a rape field are withered; on poor soil the whole crop must be at once ploughed up; but on fertile soil the plants often develop much better than one would believe. Plants whose stem has been killed in the winter while still short may develop a few (3 to 5) branches from buds situated near its base, but these usually remain small, and do not yield a large crop. The beetles, appearing in spring, lay their eggs on the lower leaf-stalks of the rape, either on the old plants of winter rape or young plants of summer rape. In the latter case the summer rape is quite spoilt in the same way as the winter rape during the previous winter. In the former case the larvæ eat out the lower part of the leaf-stalks, and make their way into the stem, hollowing it out at a definite spot in such a way that it is no longer able to hold itself up, especially when the shoots and seeds develop. The stems bend and become kneed, sometimes to such an extent that the rape field looks as if persons or cattle had been running about in it in all directions, and treading everything down. Meanwhile the larvæ bore their way out of the stem, and become pupæ in the soil. In late summer the beetles appear, and once more lay their eggs on the leaf-stalks of the winter rape. There are, therefore, two generations annually. _Remedies_: Never sow summer rape after winter rape which has been destroyed by the beetle and ploughed up. Temporary limitation of rape culture.
The =Cabbage Flea Beetle= (_Haltica oleracea_), one-fifth to one-sixth of an inch long, longish oval, dark green, metallic sheen. The hind legs do not possess the peculiar features of the rape flea beetle (p. 114). Larva one-fifth to one-fourth of an inch long, greyish black, with bristly hairs, and with two rows of shining black warts. The beetles attack, in the spring, chiefly cabbage, rape, radishes, horseradish; but do not spare other plants (_e.g._ peas and beets) as well. Seedlings are chiefly attacked, and in all cases only young plants are devoured. Since both seed-leaves and terminal buds are eaten, much damage is done, especially during continuously dry weather. It must often happen that the beetles wander away, to find other species of plants for the purpose of egg-laying; so that it is exceptional to find the larvæ upon species of cabbage. These larvæ are much less injurious than the beetles, since they usually only prey upon mature plants. In their youngest condition they are found in groups, feeding upon the leaves; this results from the eggs being laid in little heaps. Later on, they wander away from one another. In favourable weather they are fully grown in six weeks, and several generations may succeed one another in the same year. _Remedies_: Destruction of the weeds which attract the beetles (charlock, shepherd’s purse, yellow rocket, treacle mustard, etc.) Good preparation of the soil, suitable manuring and drill culture, since these bring about a more rapid growth of the plants. Thick sowing (but not too thick), so that, even after the destruction of many seedlings, a sufficient number may remain. Moistening the fields by means of water-carts or sprayers. In garden-beds twigs are laid down, by which the seeds are protected against birds and the seedlings against flea beetles. “Flea-beetle machines,” consisting of a board smeared with tar, which is drawn across the field, so that the frightened beetles spring up, and remain hanging in the sticky substance. After rain, or when dew is still clinging to the plants, they should be strewed with powdered fowls’ dung, pigeons’ dung, or horse dung, wood-ashes, road-dust, powdered lime, coal-ashes; or the plan of sprinkling with a decoction of wormwood may be adopted.
The =Turnip Flea Beetle=, or =Turnip Fly= (_Haltica nemorum_), one-tenth to one-eighth of an inch long, egg-shaped, black, with longitudinal streaks of a sulphur yellow colour on the thickly pitted wing-covers. Larva one-fifth of an inch long, yellowish white, with dark brown head, neck-shield, and last body segment. The adult beetles have the same habits as in the preceding species; they also do damage in the same way, and attack the same plants, especially in the seedling condition. The female, however, does not lay her eggs in heaps, but separately on the leaves, and always on the under side. The larva bores into the leaf, and digs a passage, which, like the animal inhabiting it, is at first small, but gets gradually larger. In fine weather the larva is fully developed in a week. It then pierces the skin covering the under side of the leaf, falls to the ground, and becomes a pupa. Several generations may appear every year, if the weather is favourable (dry). This species is quite as harmful as the preceding, chiefly in the mature condition. _Remedies_: Compare the preceding species.
Family: =Coccinellidæ= (_Lady-birds_).
Hemispherical; upper side convex; under side flattened. Head small, retractile. Antennæ, eleven-jointed, thickened at their tips. Legs short; feet apparently three-jointed—in reality four-jointed, the second joint, however, being very small. Colour, usually variegated; many species black with red, or red with black spots. When grasped, they let a yellowish, unpleasant-smelling fluid escape from the abdomen. The blunt, four-cornered, usually variegated pupæ hang on the leaves. The fully developed larvæ are longer than the beetles. They closely resemble those of the leaf beetles, but are not so thick-set, and their longer legs stick out more laterally. They are covered with warts and little spines (Fig. 85). The larvæ and beetles of most species feed chiefly on aphides and shield-lice; they are therefore of use, and this is especially true of the exceedingly ravenous larvæ. The larvæ of the Seven-spotted and Two-spotted Lady-birds, in particular (_Coccinella septempunctata_ and _C. bipunctata_), are found in large numbers among aphis colonies. The yellow eggs are laid in heaps.
SECOND ORDER: =Orthoptera= (STRAIGHT-WINGED INSECTS).
Insects with biting mouth-parts and incomplete metamorphosis (p. 89). Four wings, of which the anterior are usually harder than the posterior; hind wings membranous, broader than the fore wings, and folded like a fan. The Orthoptera feed entirely, or almost so, upon vegetable substances. To this order belong:—the =Earwigs= (_Forficulariæ_), which feed on sweet fruits and flowers, and are sometimes very injurious; the =Cockroaches= (_Blattariæ_), which do much damage to provisions in kitchens, stores, and on board ship; the =Grasshoppers= (_Acrydites_), to which, besides the =Migratory Grasshopper= (_Acrydium migratorium_) Fig. 62, various species of meadow grasshoppers belong, which are quite harmless; the =Locusts= (_Locustidæ_), to which the well-known =Green Locust= (_Locusta viridissima_) belongs; and the =Crickets= (_Gryllidæ_), to which belong, among others, the =House Cricket= (_Gryllus domesticus_), the quite harmless =Field Cricket= (_Gryllus campestris_), and the =Mole Cricket= (_Gryllotalpa vulgaris_).
The =Migratory Grasshopper= (_Acrydium migratorium_).
1⅗ to 2⅗ inches long; spread of the wing, on the average, 2½ inches. Greenish grey. Under side flesh colour. Wing-covers brownish, darkly flecked. Colour very variable (Fig. 62). Excessive multiplication and migrations of this insect often take place in South Russia and Turkey; but they may also appear in Central Europe. In North Germany, for example, the following years of this century were “grasshopper years:” 1803, 1825–27, 1853, 1875–76. In many cases the appearance of swarms of grasshoppers in Central Europe is due to migration from Russia and Hungary; but it also often happens that the insects which appear in such large numbers have been bred in the places where they are found. Since the female lays, on the average, 150 eggs, excessive increase may take place in any country to which they are indigenous—and therefore in Central Europe. It appears, however, that a large number of grasshoppers are usually killed by their natural enemies, such as cold and damp weather. Excessive increase may, however, take place in exceptionally favourable years; and since the larvæ, which are incapable of flight, devour everything available, the mature insects developed from them are forced to migrate. Where they descend they destroy everything they find in the fields. _Remedies_: Destruction of the longish eggs, which are laid in heaps in the earth of fallow ground and meadows. In all those places where dead insects are found in large numbers on the ground many eggs will also be discovered, for the insects keep on laying till they sink down dead in the place where the last heap of eggs was deposited. Such places should be dug or ploughed, and the eggs, which are present in thousands, either collected or else searched out by pigs, ducks, geese, and fowls, which have been driven to the spot. Destruction of the young animals while still incapable of flight. Working the soil with harrows, rollers, and cultivators will be effective here. The adult grasshoppers must for the most part be destroyed with fire. [Heaps of straw and brushwood are soaked with paraffin and then set on fire.]
The =Mole Cricket= (_Gryllotalpa vulgaris_).
Body stout and flattened. Antennæ, palps, and tail-filaments very long. Fore legs broad, modified into true “digging legs,” superficially resembling the feet of a mole. Fore wings broad, but short, leathery. In a state of rest, the hind wings lie on the back, like a couple of tails. Colour dark brown. Principally occurs on peaty soils mixed with sand or clay, also on all soils which have become of firm consistency by the application of much manure. Their presence is therefore local. Very early in the year the mole-cricket leaves its winter hiding-place, and begins to make its passages near the surface. Where the female makes her nest the passage turns downward a little. The nest is 1⅗ of an inch in diameter, and its walls are compacted by the pressure of the hard body. The number of eggs is from 200 to 250; they are laid in lots with a few intermediate spaces. The young creep out in the spring, and are wingless. To begin with, they are white, but quickly become brown. The mother guards her young very carefully. These grow tolerably fast, and first begin to lead an independent life after the second moult. In October and November they undergo a third moult. Then, still in a wingless condition, they hide themselves, and do not moult again till April or May, when the wing-cases appear; while after the fifth moult (May, June) the mole-cricket becomes an adult insect, capable of reproducing. This insect is found in cornfields, gardens, grassland, and meadows, also in orchards and woods. It gnaws the roots of all kinds of plants, and often effects great damage in this way. The mole-cricket is also harmful on account of its passages, which are dug close to the surface. In this way it lifts young plants out of the soil; while older plants are killed, both by its gnawing and by its digging. Such plants can often be pulled up by grasping the leaves. All the plants wither in the place where the nest is found. Dry, cold winters kill almost all the mole-crickets; much drought in summer and also continuous wet are unfavourable to them. _Enemies_: moles, rooks, etc., butcher-birds, starlings, and the larger ground beetles. _Remedies_: Destruction of the nests, in June, to begin with, but also to be continued later. In those parts of a field where the plants are yellow or withered in a large circular patch (some 39 inches in diameter) the nest is felt for with the finger, and carefully lifted up, so that the eggs do not fall out. Mole-crickets can also be caught by means of flower-pots. The apertures in the bottoms of these are stopped with corks, and they are then sunk in the soil with their mouths on a level with the mole-cricket passages; they thus serve as pitfalls, from which the insects cannot escape. If during winter little heaps of horse dung are placed on the ground, the insects creep into them for the sake of the warmth, and can thus be collected and killed.
THIRD ORDER: =Neuroptera= (NET-WINGED INSECTS).
Insects with biting mouth-parts and four similar membranous wings, with numerous veins arranged in a net-like manner. The metamorphosis is either incomplete (p. 89: dragon flies, may flies, book lice), or complete (p. 89: ant lions, lace flies, snake flies, scorpion flies, caddis flies). The indigenous forms, with the single exception of book lice, feed upon animal food, usually on the juices of other insects. Several of them are tolerably useful in this way.
The =Dragon Flies= (_Libellulidæ_) fly about incessantly from place to place on bright warm days, and catch a large number of insects, especially butterflies and flies, among which are many that are harmful. The larvæ live in water, and feed on insects and such small deer, which, however, are of no importance to forestry or agriculture. They also devour fish-spawn, and may therefore be injurious in that way.