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wards." His samples of diseased wheat-straw of the previous year yielded him, in the spring, numerous specimens of the Eurytoma, and nothing else. A few specimens of the same insect were developed from the tumors on plants of the present season, thus showing that “a small proportion of the larvæ undergo their transformations during the summer." Among his specimens he obtained a very few Hymenopterous insects, differing from the Eurytoma, and probably parasites. In several instances Professor Cabell saw a small semitransparent whitish worm, scantily covered with hairs, in the same cell with a lifeless joint-worm, and adhering to its body. In other cases, the former kind of worm or larva “was found alone, but it was then of a larger size, and there were almost always some more or less unequivocal signs of the worm having fed on the joint-worm."
Having been favored by Professor Cabell with some samples of wheat-straw, containing living joint-worms, I have been able to verify his observations during the present summer, while this sheet is passing through the press. At my request, Professor Jeffries Wyman, of Harvard College, an accomplished anatomist, and a skilful microscopical observer, has examined these larvæ, and also some of the parasitical worms, found in the straw, and has made for me several magnified sketches of them. Both kinds are found to differ essentially from the larvæ of the locust and of the willow gall-Aies, with living specimens of which I have compared them. Their bodies are softer, and their skins more delicate and tender; and the form of the head and structure of the mouth are entirely unlike those of the Cecidomyian larvæ. The true joint-worm varies from one tenth to nearly three twentieths of an inch in length. It is of a pale yellowish white color, with an internal dusky streak, and is destitute of hairs. The head is round, and partially retractile. The jaws are lateral and hooked; they meet at the points, and are of a blackish color, and apparently of a horny texture; and they are distinctly to be seen even with a pocket microscope. It is evident, therefore, that these joint-worms are not the larvæ of any Dipterous insect; they are doubtless Hymenopterous larvæ, and probably, from their abundance, those of the foregoing Eurytoma. The other larvæ, few in number compared with the joint-worms, are distinguished therefrom by their inferior size, and whiter color, and by being sparingly covered with short hairs. Their heads are round, are provided with blackish hooked jaws, and have two little tubercles on the front. I judge them to be the young of one of the parasites, probably of the Torymus, described on a
The foregoing account might be thought to afford conclusive evidence that the Eurytoma alone was the author of the mischief done to the wheat and barley, and that it is not a parasitical insect. In favor of this conclusion, we have the fact that hitherto no person has succeeded in obtaining from the diseased wheat-straw so much as a single specimen of Cecidomyia; while both the wheat and the barley straw have yielded to several observers, in repeated instances, numerous specimens of the same kind of Eurytoma, and nothing else, saving an extremely small number of lesser parasites. The determination of this difficult and interesting question is of much importance in a scientific and an economical point of view. The great amount of property that is at stake, and the serious losses already sustained by the ravages of the jointworm, render it necessary to ascertain the true history of the insect before proceeding to take measures for the protection of our crops. We are to consider, in destroying the Eurytoma, whether we shall kill an enemy or a friend. If it be a parasite, as the almost universal opinion of entomologists would lead us to believe, it would be the height of folly to attempt to interfere with its operations. On the other hand, if we can show it to be a plant-eating insect, we may use such means as are in our power towards checking its career, not only with perfect safety, but with eminent advantage. In this case, in dealing with the joint-worm, we need not be restrained by the consideration that the diseased straw contains also some truly parasitical larvæ; for these, as already stated, are very few in number compared with the immense swarms of the Eurytoma that are annually produced. If we can succeed in exterminating these destroyers, we shall have no occasion for the services of the parasites.
Admitting the Eurytoma to be the sole cause of the mischief, the following suggestions will be found useful in arresting its ravages. As the disease is seated mostly near the base of the straw, in or near the second or the third joint, the greater part of the diseased portions will be left in the stubble when the grain is reaped. Most of the insects remain unchanged in the stubble till the following year. If, then, we can destroy the maggots in the stubble before they have acquired wings and made their escape, we shall, in great measure, restrain their further propagation and increase; for it is in the winged state alone that insects propagate their kind. It has been found in Massachusetts that ploughing in the stubble has little or no effect upon the insects, which continue alive and uninjured under the slight covering of earth, and easily make their way to the surface when they have completed their transformations. The only practicable method of destroying the insects is to burn the stubble containing them. All the straw and refuse, which is unfit for fodder, should likewise be consumed, because it will be found occasionally to contain a small amount of diseased portions of the straw. Some of these may remain among the grain itself, being too heavy to be separated by the process of winnowing. These will have to be picked out by hand. Moreover, as some few of the insects are transformed to flies during the first summer, and these will suffice to continue the race, it becomes important that all the means above recommended should be continued during several successive years; and when these are universally, carefully, and thoroughly put in practice, they can hardly fail to exterminate the Eurytoma. A free use of manure and thorough tillage, by promoting a rapid and vigorous growth of the plant, may render it less liable to suffer from the attacks of the insect. Large fields, well seeded, will probably escape better than those that are smaller and thinner sown, in which the insects, when about to lay their eggs, can penetrate easily and to a greater distance.
GNATS AND FLIES. — Maggots, AND THEIR TRANSFORMATIONS. GALL-Gxats.
Hessian Fly. Wheat-Fly. — REMARKS UPON AND DESCRIPTIONS OF SOME OTHER DIPTEROUS INSECTS. – RADISH-F14. - Two-WINGED GALL-FLIES, AND FRUIT-FLIES. CONCLUSION.
UNDER the name of DIPTERA, signifying two-winged, are included all the insects that have only two wings, and are provided with two little knobbed threads in the place of hind wings, and a mouth formed for sucking or lapping.
Various kinds of gnats and of flies are therefore the insects belonging to this order. The proboscis or sucker, wherewith they take their food, is placed under the head, and sometimes can be drawn up and concealed, partly or wholly, within the cavity of the mouth. It consists of a long gutter, usually ending with two fleshy lips, and enclosing, in the channel on its upper side, several fine bristles, from two to six in number, which are sometimes as sharp as needles, and are then capable of inflicting severe punctures. These piercing bristles really take the place of the jaws of biting insects, and hence the wounds made therewith, by gnats and mosquitos, are very properly called bites. The saliva of these insects flowing into the wounds, renders them more painful, and is the cause of the inflammation and itching that follow. The grooved sheath of the proboscis is usually very large and fleshy in the flies that only lap or sip their food. Two small, jointed feelers are commonly found attached to the base of the proboscis. Gnats and flies have softer bodies than most other winged insects. The head is large, and fastened to the thorax by a very slender neck. The eyes, especially in the males, are large, and occupy the whole of the sides of the head. The antennæ, in gnats and mosquitos, are rather long, slender, and many-jointed; in flies, they are short, consisting of only two or three thick joints, the last of which often bears a little bristle or delicate feather. The wings are filmy, like those of Hymenopterous insects, but usually have a greater number of veins in them. Just behind the wing-joints there are two little, convex scales, which open and shut with the motion of the wings; they are called the winglets. The two balancers or poisers are short threads, knobbed at the end, and placed on each side of the hindmost part of the thorax, immediately behind the winglets. The thorax is often the thickest and hardest part of the body; to it the hind body is more or less closely united, and the latter, in many females, ends with a tapering, retractile tube, wherewith the eggs are deposited. The legs are six in number, and each of the feet is provided with two claws, and two or three little cushions or skinny palms, by the help whereof the insects can walk on the smoothest surfaces, and on the ceilings of rooms, with the back downwards, as easily as when upright; for the palms act like suckers, and thus prevent them from falling
Mosquitos and gnats are active both by day and night, but flies take wing only during the day. The life of these insects, even from the time when they are first hatched, is generally very short, seldom lasting more than a few weeks; but of some kinds several broods are produced in the course of a single summer, and often in the greatest profusion. In certain countries and seasons they multiply so fast, and appear in such immense swarms, as to become a serious annoyance both to man and beast.
The young insects, hatched from the eggs of gnats and of flies, are fleshy larvæ, usually of a whitish color, and without legs. They are commonly called maggots, and sometimes are mistaken for worms. They vary a good deal in their forms, structure, habits, and transformations, so that it is somewhat difficult to give any general description of them. Their breathing holes are usually situated near the extremities of the body. Aquatic maggots often have a tubular tail, through which they breathe, and the orifice of this tube is sometimes surrounded with beautiful feather-formed appendages. The larvæ or maggots of the gnats, and of nearly all those flies which have four or six bristles in the proboscis, have a distinct