156 The Hessian Fly, and its Parasites. 



larva will do little harm, (and may even be useful by stimulating 

 the plant to throw out side shoots,) but five or six of them are 

 sufficient seriously to check the growth of the plant, or perhaps 

 to destroy it entirely.* 



During the winter the insect is in the pupa state, near the 

 root of the wheat plant, and usually a little below the surface of 

 the earth. In April and May we again find the Hessian fly lay- 

 ing eggs on the young wheat, both that which was sown in the 

 autumn previous, and the spring wheat, which is of course re- 

 cently up. The larvae from these eggs become pupae about the 

 middle of June. 



There is no difficulty in tracing the insect as far as the state of 

 pupa, and to this point its history is satisfactorily ascertained. 

 Regarding the periods of the evolution of the perfect insect, there 

 is, however, some obscurity, which numerous observations have 

 not wholly cleared up. The difficulty results in part from the 

 fact that in this region, a very large proportion, probably more 

 than nine tenths^ of every generation of the Hessian fly, is de- 

 stroyed by parasites. A great part of the pupse which may be 

 collected will evolve some parasitic insect, instead of the Hessian 

 fly. It is certain that sometimes, the pupae, which became so in 

 June, evolve the perfect insect in October following, and that 

 other pupse of the same date will not evolve the perfect insect 

 until October of the year succeeding. The following seems to 

 me the probable history of the matter. The pupse, which be- 

 came such in the autumn, evolve the perfect insect, partly during 

 the next spring, and partly in the summer and autumn following. 



* It has been repeatedly asserted that the Hessian fly lays lier eggs on the ripen- 

 ing grain. This error has doubtless arisen from mistaking for the Hessian fly, 

 other insects, which in various parts of our country attack the wheat. In the Trails, 

 of the £.mer. Phil. Soc, 1771, i, 205, Col. Landon Carter has given some account 

 of a pale brownish moth, called by him the fly weevil that destroys the loheat, which 

 lays its eggs on the grain. A paper on what is probably the same insect, is pub- 

 lished by John Lorain in Mease's Archives of Useful Knowledge, 1812, ii, 47. The 

 insect is supposed to be that described by Duhamel du Monceau in his " Histoire 

 d'un Insecte qui devore les Grains de I'Angoumois," Paris, 1762. 12mo. — the CEco- 

 phora cerealella, Oliv. I have little doubt that the Tipula (Cecidomyia) Tritici^ 

 Kirby, {Trans. Linn. Soc. iii, iv, v,) also inhabits this country. — In August, 1833, 

 I received several stalks of wheat from West Chester, Penn., each containing, in 

 the centre, a small larva of a wax-yellow color; but I failed to obtain the perfect 

 insect. It is hardly necessary to say that this was not the larva of the Hessian 

 fly. A critical investigation of all these insects is very much to be desired. 



