/ 
Seigeoun STATES DEPARTMENT OF AGRICULTURE... : 
BULLETIN No. 1008 ¢ 
Contribution from the Bureau of Entomology as , \ 
L. O. HOWARD, Chief 
Washington, D. C. PROFESSIONAL PAPER November 15, 1921 
RATE OF MULTIPLICATION OF THE HESSIAN FLY. 
By W. R. McConneELL,. 
Entomological Assistant, Cereal and Forage Insect Investigations. 
CONTENTS. 
; Page. Page. 
. Introductory and historical___-_--~_~- 1 | Average number of ova for the prin- 
Methods -of investigation__________ 2 cipal broods—Continued. 
Average number of ova for the prin- Summer generation___~-______ 5 
Pipa mPrOOUss nec. eT 4 POY SD: aN Ma ez {0 gam LY cn dak Al ll 6 
Malt seneratiqn: 22) soe te 4 | The meaning of these figures______ 6 
Spring generation____________ Ss} Corn Cl SPO rn Se ee GA 8 
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 importantgpatural checks to the 
increase of the fly, suspected nevertheless thet 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 
' 1Died June 23, 1920. 
» G5675°2— 21 
