February, '17] 



DEAN: HESSIAN FLY 



147 



suffering heavy losses from the Hessian fly that may reach sixteen 

 million dollars, as in 1915, the time of seeding to produce the maxi- 

 mum yield and the time of seeding to escape the fly are two of the most 

 important factors in growing wheat. 



''There can be no doubt that the seasonal periodicity so charac- 

 teristic of animals and plants generally is exhibited in both the Hessian 

 fly and its host plants — that there is a period of time in the fall during 

 which, under normal conditions of food supply, the emerging flies 

 have the best possible opportunity to perpetuate their kind and that 

 there is likewise a period during which wheat placed in the soil stands 

 the best chance to produce the maximum yield. This period may be 

 designated as the normal time of fall-brood fly emergence and the normal 



Fig. 5. Map of the state of Kansas showing stations of the last ten years. 



time for wheat sowing, respectively. The problem of determining when 

 wheat should be sown to escape the fall brood of the Hessian fly involves 

 the explanation of the relationship existing between the normal period 

 of fly emergence and the normal period of wheat sowing." ^ 



In order to secure data bearing on the problem, a series of experi- 

 mental sowing was begun in 1907 by Dr. T. J. Headlee, then ento- 

 mologist of the Kansas Experiment Station. These sowings have now 

 extended over a period of ten years, and it is planned to . continue 

 them over another period of ten years. The' sowing in 1907 consisted 

 of a single series of stations extending along the eastern edge of the 

 wheat belt from the northern to the southern part of Kansas, but all 

 subsequent sowings consisted of a double series of stations, one along 

 the eastern and one along the western edge of the great central wheat 

 belt. The individual stations of the eastern series are located from 



1 Headlee, T. J., Journ. Econ. Ent., p. 98, vol. V, No. 2, 1912. 



