152 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



food supply disappears, almost all develop wings, and immense 

 clouds of the winged females are carried northward by the 

 winds, so that an outbreak in early spring in the South leads to an 

 infestation farther north, and excessive multiplication will again 

 carry the pest still northward, progressing in that direction as it 

 increases during the season, rather than being spread at one time. 

 Thus in 1907 it became abundant in Oklahoma in April, in Kansas 



FIG. 111. Green bugs on oat-seedling enlarged. 



in May, and by July it was found in Minnesota, where it rarely 

 occurs and does no damage. With the maturing of wheat and oats 

 the aphides migrate to various grasses, being particularly fond of 

 Kentucky blue-grass, and may subsist on corn, on which they 

 may feed until oats and wheat are available in the fall. Oats are the 

 favorite food, and outbreaks of the pest have always been worst 

 where volunteer oats are generally grown, the aphides increasing 

 on them in the early fall and winter and later spreading to wheat. 

 By October loth in Minnesota and by early November in Kansas 

 the true winged males and wingless egg-laying females have been 



