258 Effect of the early soicing of Wheat on the Hessian Fly. Vol. XII. 



liable to be injured by the fly as that which 

 is .sown earlj', militate against this conclu- 

 sion ; for the principal darnao-e to the wheat 

 crop is mostly done by the spring brood, and 

 it the fly is in the neighbourhood it will be 

 as likely to lay its eggs in that which was 

 sown liite as in any other. Nay, it is not 

 improbable that the younger plants furnished 

 by the late sowing, may be preferred by it; 

 and that to such it will be more destructive 

 than to those which are older and more vig. 

 orous. Thus he who by sowing early, raises 

 a plentiful winter brood of these insects, 

 cherishes an enemy which is quite as likely 

 to destroy his neighbour's crop as his own. 

 There is therefore no security to be found 

 in late sowing when practiced by a few, 

 while the general mass sow early enough to 

 allow of tiie egg to be deposited in the 

 young plants before the season of the fly is 

 past. If anything is to be gained by the 

 practice in the way of preventing the mul- 

 tiplication of the fly, it must be universally, 

 or at least very generally adopted. 



With regard to the other branch of the 

 proposed enquiry, — whether a continuation 

 ot the practice of early sowing will occasion 

 the continued destruction of the wheat crop 

 — there is a curious fact connected with the 

 life of the Hessian fly, which it is very ne- 

 cessary to take note of. 



This destructive pest has a deadly enemy 

 in a parasite insect of nearly its own size, 

 by which myriads of its kind are every year 

 destroyed. This enemy attacks the fly about 

 tiio time when it assumes the brown cover- 

 ing, or perhaps somewhat earlier. It depos- 

 ites its egg in, or on the bodyoftlie fly, where 

 it hatches, and the young larva proceeds to 

 feed itself thereon till it eats it all up, and 

 occupying the shell which the fly had pro- 

 vided for itself, it goes through its appointed 

 changes, and in due time comes forth a 

 winged insect, prepared to seek out a place 

 for its progeny similar to that in which it 

 was nurtured. These insects may be seen 

 coming forth from a portion of the shells 

 which the Hessian flies had prepared for 

 themselves, about two or three weeks after 

 the time wlien the Hessian fly makes it ap- 

 pearance. They are assiduous in seeking a 

 suitable place to deposite theireggs, of which 

 on one occasion I had a striking illustration. 

 I had gathered some stalks of grain contain- 

 inir the fly at the time of harvest, and put 

 them in a glass ves.sel in an open room used 

 fordrying and preserving seeds. I intended 

 to cover them up and watch their develope- 

 ment, but being then much engaged, I left 

 the vessel uncovered. On returning to it a 

 few days after, I observed a number of those 

 enemies of the Hessian fly — with whose ap- 



pearance I had previously been somewhat 

 familiar — gathered about and on the straw 

 in which the flies were enveloped, as if they 

 were attracted there by something peculiar. 

 Indeed they were evidently seeking a place 

 to deposite their eggs. 



Through the agency of this parasite a 

 large proportion of the Hessian flies are 

 every year destroyed, and it is highly proba- 

 ble that but for this destruction we should 

 be utterly unable to raise wheat to profit. 



Now it is manifest that the destruction of 

 the Hessian fly will be increased as the num- 

 ber of its enemies is multiplied; and it is 

 evident that these will multiply more or less 

 according to the means of their subsistence. 

 Whenever the Hessian fly is abundant, it 

 furnishes the means for the multiplication 

 of its enemies, and this increase of the para- 

 site insect is only checked when the destruc- 

 tion of the fly limits its supply of food. Thus 

 when any circumstances give peculiar en- 

 couragement to the increase of the Hessian 

 fly, its power of increase is so great it soon 

 multiplies to the extent of its means of ob- 

 taining suitable situations for its brood, or at 

 least it makes rapid strides towards this con- 

 dition. Its enemy however is not much its 

 inferior in such a race; but it cannot start 

 until the other by its abundance has fur- 

 nished it with the means. It then continues 

 to multiply so long as these means are fur- 

 nished, and it continues to hunt down the 

 Hessian fly with unwearied assiduity, till a 

 scarcity of its appropriate food arrests its 

 further progress and thins its ranks. Its di- 

 minished numbers cease to be formidable to 

 the Hessian fly, and allow it to take advan- 

 tage of the first favourable chance to start 

 forward in another race — again it is pursued, 

 overtaken, and hunted down by its unwea- 

 ried adversary, and again that adversary 

 partly perishes for the want of food — and 

 thus a constant succession of floods and ebbs 

 in the tide of being is naturally produced, 

 in this department of the insect world. 



In accordance with these principles, we 

 find that when the Hessian fly first made its 

 appearance in our country, it was for some 

 years much more destructive than it has 

 been at any time since; and that the visita- 

 tions of this plague since that time, have 

 been of a more or less periodical character. 



We may conclude, therefore, that the 

 practice of sowing wheat early in the sea- 

 son, has for some years past given an im- 

 petus in this district to the increase of the 

 Hessian fly, which has enabled it to outstrip 

 the pursuit of its destroyer, and to devastate 

 our wheat fields; but we may rest assured 

 that this state of things will not continue 

 many years. The abundance of the Hessian 



