INSECTS INJURIOUS TO WHEAT. 103 



also reveal their presence. Later, many of the plants may 

 be observed to turn yellow and die. The spring maggots 

 attack the laterals, or tillers, which have escaped the 

 previous brood, so weakening them that the stems break 

 and fall before ripening, and cannot be readily harvested. 



In about four weeks the maggots become full-grown, 

 and are then light greenish white and about three-sixteenths 

 of an inch long. The skin now turns brown, shrivels 

 slightly, and inside of it is formed the new stage, called 

 the pupa. This outside case, composed of the cast larval 

 skin, is known as the puparium, and this stage is generally 

 called the '' flax-seed '^ stage from the close resemblance to 

 that seed. In this stage the fall brood passes the winter, 

 the flies emerging in April or May, while the spring brood 

 so remains during midsummer, and emerges during Sep- 

 tember. Besides the above, there are often two supple- 

 mental broods, one following the spring brood, and the 

 other preceding that of the fall. 



Enemies. — Several parasites arc of great value in hold- 

 ing the numbers of the fly in check, but as yet no method 

 is known whereby they mry be artificially encouraged. 

 Attempts to import foreign parasites have not, as yet, been 

 permanently successful. It is owing to these parasites 

 being destroyed by unfavorable weather conditions that 

 the fly becomes excessively abundant. 



Preventives. — Owing to the wide distribution of this pest, 

 and the corresponding variation of latitude and altitude, 

 it is evident that the time of its appearance will varv con- 

 siderably, and any 2:>reventive measures must be based upon 

 a previous determination of the time of appearance of the 

 broods for any given locality. Recently it has been shown 

 that weather conditions largely determine the time of 



