INSECTS INJURIOUS TO SMALL GRAINS 



119 



so weakening them that the stems break and fall before ripening 

 and cannot be readily harvested. 



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 "pupa- 

 rium," and this stage 

 is commonly called the 

 "flaxseed" 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 during 

 the late summer and 

 emerges when the first 

 wheat is planted in the 

 fall, emerging later far- 

 ther south. 



Several species of 

 small chalcis flies (page 

 19) parasitize the larvae 

 and pupae and were it 

 not for their assistance 

 it would doubtless be difficult to raise wheat. As yet no prac- 

 tical 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- 



FIQ. 100. "Flax-seeds" or puparia of the Hes- 

 sian fly on young wheat enlarged. (After 

 Pettit.) 



