PLANT LICE INJURING THE FOLIAGE 197 
grown and thus have acquired tougher leaves, the lice develop a winged 
generation, leave the section where at work, and appear as suddenly in 
other regions farther north, where conditions are favorable to further 
multiplication. 
Late in summer, as the grain fields mature, the lice leave them and 
take up their residence on grasses, such as common bluegrass or on corn. 
In the fall, when winter grain has sprouted, many move back to the new 
feeding ground. With the coming of cold weather, eggs are laid 
among grain plants. In the more Southern states there are living 
Fic. 246.—The Spring 
Grain-aphis. Wing- 
Fig. 245.— The Spring  Grain-aphis. less form. Enlarged 
Winged adult. Enlarged and natural and naturalsize. Orig- 
size. Original. . inal. 
females in existence all winter. The insect isable to breed at unusu- 
ally low temperatures. 
Oats and wheat are the favorite food plants, but the list includes rve, 
barley, corn, and several species of wild grasses, especially orchard grass. 
Normally this insect is held in check by its natural enemies, especially 
by a four-winged parasite which attacks the lice, laying its eggs within 
their bodies. Severe attacks follow warm winters combined with cold 
springs — a condition unfavorable to the parasite, but favorable to the 
aphis. 
Direct control is not feasible. Cleaning up volunteer oats and other 
food plants in the fall will greatly reduce the numbers the following 
spring. Attempts have been made artificially to introduce the parasite, 
but without entire success. 
