INSECTS INJURIOUS TO WHEAT. 117 



thinks that cold, wet weather in May and June is favor- 

 able to the lice, in that it retards the development of their 

 parasites. 



Description and Life-liisiory. — The first individuals are 

 found on the young wheat in the latter part of April, 

 though during open winters they may remain on the 

 young wheat, as observed by Dr. Cyrus Thomas in 1875 

 and Prof. H. Garman in 1889. Until early July the lice 

 feed upon the wheat, first upon the stalk and leaves and 

 later upon the head, breeding in the parthenogenetic 

 manner of most aphids. (See life-history of Corn Eoot- 

 aphis, page 13G.) The color of the lice varies greatly, as 

 does also the size. In the spring the winged lice are 

 green, with head, antennae, thorax, femora, tarsi, corni- 

 cles, and a series of spots on the sides of the abdomen 

 black. As the grain matures and the lice migrate to the 

 head, many of them become yellow, reddish, and some of 

 the winged forms almost black. The wingless lice are of 

 a pale green. 



Oats, barley, rye, corn, blue grass, and many other 

 grasses furnish food for this pest, and after the wheat 

 becomes mature it may commonly be found on volunteer 

 oats until the fall wheat appears. During the hot weather 

 of midsummer, however, it is not much in evidence. 



The true sexes occur in the fall, and eggs are laid upon 

 the fall wheat. 



Enemies. — "Were it not for its parasites and the preda- 

 ceous insects which feed upon it, the Wheat-aphis would in- 

 deed be a most serious past, but ordinarily these keep it well 

 under control, and when for some reason they are them- 

 selves killed off for a season and the lice have opportunity 

 to multiply, they soon become so numerous as to again 



