30 



the flies, wliich these frosts will kill if in the imago stage. If, 

 however, these winged flies have already bred in volunteer and 

 early wheat, and if the early frosts find the insect in the hardy 

 stage of larva or puparium, the flies emerging from these, as they 

 mature, will often make their appearance hciiccen frosts and deposit 

 their eggs on the yonngest wheat accessible, before being overtaken 

 by killing cold. As late wheat is then in a condition more tempt- 

 ing to the mother than that in earlier sown fields, it is, on the 

 whole, more likely to suffer serious injury. 



It seems to be sometimes the case, however, that a field of 

 early wheat infested in autumn, in the usual way, will develop the 

 imago of the regular autumnal brood so early that it may be 

 again attacked by the second autumnal brood and destroyed before 

 cold weather arrests the ravage. Whether, consequently, the wheat 

 be sown early or late, it is very evidently important that particu- 

 lar attention be paid to the volunteer wheat in regions subject to 

 injury by the fly. If the land w^ere so handled that the volunteer 

 wheat,' rye, and barley were not allowed to spring up, or if they 

 w^ere killed everywhere as fast as they should appear, no midsum- 

 mer brood could develop, and the fall grain w^ould be much less 

 liable to attack. The late wheat especially w^ould be protected, 

 and late sowing would have the desired effect.* 



Neither spring wheat nor barley are raised in Southern Illinois, 

 but it may be proper to add that if they were, they would greatly 

 complicate the problem of protecting the wheat from the Hessian 



fly- 



I believe, however, that a more valuable use of the facts in the 

 case may be made than this. Although our knowledge of the fly 

 does not lead us to believe that it is perfectly three-brooded, and 

 does not even justify us in assuming that all the winged flies 

 coming out before and soon after harvest will deposit their eggs 

 in volunteer wheat if this is offered tbem, yet it is certain that a 

 large part of them will do so; and our recent observations indicate 

 that the residue w^hich will, under these circumstances, delay their 

 ovii)psitiont until a moderately late sowing time, is so small that 

 it w^ould be unlikely to do any great harm. Or, in other words, 

 our present information warrants us in saying that if the fly is 

 given an opportunity to breed in volunteer w^heat, and if the 

 progeny resulting are destroyed before the transformation to the 

 winged insect, damage by the fly w^ould be greatly lessened, if not 

 practically prevented, in the latitude of Southern Illinois. 



The mode of procedure which " here naturally presents itself is 

 such a management of the land as will, first, encourage the growth 



•A dry Beason is usually favorable to Insect development, but the ITessinn fly has been consid- 

 ered an exception to this very fteneral rule. It seems possible that this soemlnK'y detrimental in- 

 fluence of dry weathor may be due to the failure of volunteer wheat, and the consequent supprossion 

 of tiie summer brood. 



l it 1h by TnoRt writers believed that the female Imaffo cannot delay oviposition. but that liv- 

 ing: only a fovv days, she must lay her eggs at once, whether conditions are favorable to their de- 

 velopment or not. 



