158 



EXPERIMENT STATION RECORD. 



under, the destruction of volunteer wheat, and late sowing. " The sources of 

 the flies which form each of the broods are variable, for the members of a single 

 brood came from as many as three different places— old stubble, regular crop, 

 and volunteer wheat. The measures of control must be of such a nature as to 

 close up all these sources of supply. Temperature and moisture are the only 

 climatic elements that appear materially to influence the fly. Low temperature 

 or low moisture, or both acting simultaneously, always retard its development, 



1^ = PUP/l/^//l /A/ REGUL/}^ C/^OP. 



n = PUP/^p//i /A/ \/olunt£:er ia/he/^t. 



DHH = PUP/iP//^ /A/ OLD STUBBLE. 



mm = REGULAR BROODS . 



mm = SUPPLEA^EAJT^RY BROODS, 



Fig. 1. — Diagram to represent the number of broods of Hessian fly in Kansas in 1908, 

 the period of their appearance, and the sources from which they came. 



and may, if extreme, destroy it. High temperature and high moisture are uni- 

 versally favorable to its development. Although both predaceous and parasitic 

 enemies always reduce the fly, their action is so irregular and so rarely sufiBcient 

 that dependence upon them for protection is folly ... In the fall the central 

 shoot of the young plant is stunted and killed ; if the attack be serious enough, 

 the whole plant and the whole field may be destroyed. Ordinarily the slow de- 

 struction of the central shoots causes the tillers to grow vigorously, giving the 



