THE MONTHLY BULLETIN. 



69 



legs and antenna being black and the remainder green). Like the 

 apterous forms they have power to produce both winged and wingless 

 forms. 



The appearance of the winged individual is very significant in that 

 this migratory form is the principal means of distribution and of the 

 formation of new summer colonies. Many plant lice winter over on 



Fig. 56. — The green apple aphis ( Ajihis pomi DeGeer) infesting young 

 apple shoot.s. (After U. S. Dept. Agrcl.) 



fruit trees as does the hop louse, and the winged forms later migrate 

 to the hop fields and produce the l^roods which so trouble the hop 

 liTowers. Late in the fall the winged forms migrate back from the 

 liop fields to the plum and produce the egg-laying females which 

 deposit their eggs on the trees. The eggs give rise to the next year's 

 broods. 



