CECIDOMY'IA, a genus of Two- Winged Flies, belonging to the order Diptera and the family Tipulidce. It is known by the following theracters :—Wings resting horizontally, and having 3 longitudinal lervures; head hemispherical : antenna as long as the body, and ;enerally 24-jointed, the joints hairy (in the females 14-jointed); the 2 basal joints short; legs long, basal joint of the tarsi very short, second long.
Mr. Stephens, in his Catalogue of British Insects,' enumerates 26 species of this genus. They are always of small size, and many of them deposit their eggs on the young buds of various kinds of plants, where the larva is hatched, and transforms them into galbi, in which it subsists and undergoes its metamorphosis.
C. salicina is common in France on willows in the month of May; it is of a blackish colour, covered with fine velvet-like hairs ; the antenna have 20 joints ; the wings are slightly obscure and downy ; length one-sixth of an inch.
This little fly fixes each of its eggs on a bud of the willow in the month of June. The bud at the time of its evolution, near the end of the month, instead of putting forth its branch, becomes enlarged at the base, and ultimately forms a gall in which the larva is lodged, nourishcd, and undergoes its metamorphosia : the larva is of a reddish-yellow colour, and assumes the pupa state in the winter, when the gall is become of a large size.
Other species of Cecidomyia produce similar deformities upon various parts of many species of plants, and resemble in this part of their habits the Cynipidee among the Hymenoptera.
C. Tritici (Tipula Tritici, Kirby), an insect commonly known by the name of the Wheat-Fly, has occupied much of the attention of entomologists. Kirby published two accounts of its habits in the Linnman Transactions' (vol. iv.).
This little fly is about one-twelfth of an inch in length, and of a reddish-yellow colour; the wings are milk-white, and exhibit the prismatic colours in certain lights : the eyes are black. The Wheat Fly may be observed sometimes in the greatest abundance flying about wheat-fields in the month of June. It generally makes its appearance about seven or eight o'clock in the evening. "Although," says Mr. Kirby, "these insects are so numerous in the evening, yet in the morning not a single one in to be seen upon the wing ; they do not however then quit the field which is the scene of their employ ment, for upon shaking the stalks of the wheat or otherwise disturb ing them they will fly about near the ground in great numbers. I
found their station of depose to be upon the lower part of the cuhn with their heads upwards." The fly totally disappears by the end of June. According to Kirby, it in about eight o'clock in the evening that they deposit their eggs. He has seen as many as twelve speci mens thus occupied at the same time on a single ear, and observes that these flies are sometimes so numerous that, were all to lay their eggs and these to hatch, one-half of the grain would be destroyed.
The eggs are deposited by meana of a long pointed and contractile tube, or ovipositor, generally upon the interior valvule of the corolla, just above the stigmata ; and it occasionally happens that the fly is unable to retract its ovipositor, and being thus held prisoner it dies.
About the middle of June the larva are hatched, and may be seen adhering to the lower end of one of the anthers, and sometimes immersed in the woolly summit of the german, or in the interior of the valvulte of the corolla. These larva are simple minute grebe, without legs or any visible head, and of a yellowish colour; and their food consists of the pollen of the anthers, which it appears in the plants thus attacked is unfit for impregnation.
The pupa are of a reddish colour, and in number bear no proportion to that of the larva. " I have seen," nays Mr. Kirby, " more than once, seven or eight florets in an ear inhabited by the latter, and sometimes so many as thirty in a single floret, seldom leas than eight or nine, and yet I have scarcely ever found mere than one pupa in an ear, and had to examine several to meet with that. . . . . The pupa that I have observed have generally been somewhat attached to the grain, and, what is worthy of notice, I never observed them within those florets where the larva) had taken up their residence ; they seem invariably to choose for their habitation, in their immediate state, one where the grain is uninjured, to which they may attach themselves." In a field of 15 acres (planted partly with white and partly with red wheat), which Mr. Kirby carefully examined, and which was much attacked by these insects, he calculated that the havoc done by them would amount to five combs ; he observed that the white wheat was most effected.