182 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



THE WESTERN WHEAT APHIS (BRACHYCOLUS TRITICI 



GILL.) 



By J. R. Parker, Bozeman, Mont. 



Historical 



The Western wheat aphis was originally described by Professor 

 Gillette in Entomological News for December, 1911. Concerning it he 

 remarks, "This is seemingly a rather rare species occurring upon 

 grasses and has been taken several times by L. C. Bragg upon the leaves 

 of blue stem {Agropyron glaucum) and upon wheat during the summer 

 months in the vicinity of Fort Collins." 



In Montana this insect first attracted attention in 1910 when re- 

 ports came to the experiment station that a plant louse was destroy- 

 ing winter wheat in a few localities in Fergus County. An investiga- 

 tion of these reports brought out the fact that more injury was being 

 done than we had believed a grain plant louse capable of doing. In 

 one instance a grower who had 700 acres of wheat estimated his loss 

 due to wheat aphis at 5,000 bushels. Another grower had 80 acres of 

 winter wheat so badly injured that no attempt was made to harvest it. 



Since 1910 the Western wheat aphis has become increasingly abun- 

 dant in Fergus County and has appeared in injurious numbers in 

 several other counties. During the past two seasons in Montana, 

 with the exception of the army cutworm (Chorizagrotis agrestis Grote), 

 it has ranked as the most destructive insect pest of winter wheat. 



Since economic entomological literature contains no account of the 

 Western wheat aphis, and because of the great economic importance 

 of its host plant, this paper has been prepared to bring together some 

 of the facts which have been learned about this new pest of wheat. 



Description 



Technical descriptions of the various forms of this species have been 

 published by Professor Gillette in Ejitomological News, Volume XXII, 

 pages 441-442. In this paper only a brief general description will be 

 given. 



The wingless viviparous female, which is the form most frequently 

 seen, is peculiarly shaped, being unusually long and narrow for an aphid. 

 It is about 2 millimeters in length, and .6 of a millimeter in width. The 

 general color is a pale yellowish green, but this is generally hidden by a 

 powdery white coating. The body appendages are all somewhat 

 reduced: the cornicles can be seen only with the aid of a lens; the an- 

 tennce are less than half the length of the body and the legs are quite 



