UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 1008 



Contribution from the Bureau of Entomology 

 L. O. HOWARD, Chief 



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Washington, D. C. 



PROFESSIONAL PAPER 



November 15, 1921 



RATE OF MULTIPLICATION OF THE HESSIAN FLY. 



By W. R. McConnell, 1 

 Entomological Assistant, Cereal and Forage Insect Investigations. 



CONTENTS. 



Page. 



Introductory and historical 1 



Methods of investigation 2 



Average number of ova for the prin- 

 cipal broods 4 



Fall generation 4 



Spring generation 8 



Page- 



Average number of ova for the prin- 

 cipal broods — Continued. 



Summer generation 5 



Sex ratio . 6 



The meaning of these figures 6 



Conclusions & 



INTRODUCTORY AND HISTORICAL. 



In the course of investigations of the Hessian fly (Phytophaga 

 destructor Say) and its parasites, at the Cereal and Forage Insect 

 Field Station of the Bureau of Entomology at Carlisle, Pa., it be- 

 came necessary to have accurate data regarding the normal rate of 

 multiplication of this insect. Such information was needed, in the 

 first place, as a basis for estimating the efficiency of the various 

 species of parasites. In the second place, the writer, having been 

 greatly impressed by the rapidity with which an outbreak of serious 

 proportions may develop in a short time from comparatively small 

 sources, and being aware that such an increase is largely due to the 

 reduction in effect of some of the important natural checks to the 

 increase of the fly, suspected nevertheless that the potential rate 

 of multiplication might be much greater than usually has been sup- 

 posed. 



The writer has been unable to find satisfactory data on this subject 

 in the literature or among other recorded observations. In fact, it ap- 

 pears that little attention has ever been paid to the matter, especially 



*Died June 23, 1920. 

 65675°— 21 



