INSECTS INJURIOUS TO SMALL GRAINS 



125 



stems break and fall before ripening and cannot be readily har- 

 vested. 



About four weeks after hatching the maggots are full grown, 

 and are greenish-white and about three-sixteenths inch long. The 

 skin then turns brown, shrivels slightly, and inside it is formed the 

 pupa. This outside case, composed of the cast larval skin, is known 

 as the " puparium," and this stage is commonly called the "flax- 

 seed " from the resemblance to that seed. .In this stage most of 

 the fall brood passes the winter, the flies emerging in April or May, 

 while the summer 

 brood remains in 

 the "flaxseed?' stage 

 in the stubble dur- 

 ing the late sum- 

 mer and emerges 

 when the first wheat 

 is planted in the 

 fall, emerging later 

 further south. 



Several species 

 of small chalcis flies 

 (page 19) parasitize 

 thelarvseand pupae, 

 and we're it not for 

 their assistance it 

 would doubtless be 

 difficult to raise 

 wheat. As yet no 

 practical method 

 of increasing their abundance has been devised, though colonies 

 have been carried to regions where they were scarce. 



Control. The principal means of avoiding injury by the Hes- 

 sian fly in the winter wheat regions is late planting in the fall. 

 Inasmuch as the flies appear within about a week and then dis- 

 appear, if planting be delayed until after that time, but little of the 

 wheat will be injured. Dry weather in late summer and early 



FIG. 91. The Hessian fly, adult male greatly 

 enlarged. (After Marlatt, U. S. D. Agr.) 



