90 FARM FRIENDS AND FARM FOES 



in summer on various grains and grasses, and migrates in 

 autumn to apple trees, where the winter eggs are laid. 

 Consequently, when we attempt to follow its history through 

 the year, we may begin in early spring with these eggs 

 upon the buds and bark of apple twigs, with this summary 

 as a result : 



In early spring the eggs hatch into small aphides that 

 crawl at once to the developing buds where they begin to 

 suck the juices of the unfolding leaves. In a few days, 

 this first generation from the egg, often called the stem- 

 mothers, begin giving birth to living young that also suck 

 the sap from the leaves and soon become mature. In this 

 way, four or five generations may develop on the apple in 

 spring. A large proportion of the later generations are 

 winged females, which fly away to settle upon grasses and 

 grains and start colonies upon these host plants. Conse- 

 quently these are called winged migrants. As a rule, all 

 of the plant lice of this species thus desert the apple before 

 midsummer. 



The winged migrants upon grains and grasses establish 

 colonies that continue to increase throughout the remain- 

 der of the summer upon these food plants, one generation 

 following another in rapid succession. Rather early in 

 autumn, however, a generation of winged females, called 

 the return migrants, is developed from the grain and grass- 

 feeding colonies. These return to the apple, where they 

 give birth to a generation of wingless egg-laying aphides, 

 by which the winter eggs are laid upon twigs. 



There are various other species of aphides which may be 

 found upon the leaves of the apple. The presence of these 

 other species has rendered the working out of the life his- 

 tory of this European Grain Aphis a much more difficult 

 problem than might at first appear. 



