152 MANUAL OF VEGETABLE-GARDEN INSECTS 



cornicles reticulate for a short distance instead of being im- 

 bricated throughout. At the approach of cold weather, 

 the winged forms migrate to the rose and there produce a 

 generation of winged males and wingless egg-laying females. 

 In Maine the winter eggs are laid in late September. 



Fig. 88. — The wingless viviparous female potato aphis ( X 7^). 



The time at which the pest becomes destructive to potatoes 

 varies from year to year. In Maine it has been found most 

 abundant in August, but in 1917, w^hen the outbreak was the 

 most extensive and destructive so far recorded, the attack be- 

 came serious in New York in early July and in Ohio in late 

 June. On potatoes the aphids cluster on the underside of the 

 leaves, causing them to curl downward. They also infest 

 the tender tips and the blossom stems. When badly infested, 

 the vines soon become covered with the sticky honey dew 

 secreted by the aphids. The tips are first killed, and in 1917 

 many large fields were observed in which all the plants were 

 killed to the ground. Even when the vines are only partly 

 killed, the size and quality of the crop is seriously affected. 

 On tomatoes the lice also infest the leaves but cause their 

 greatest injury by attacking the blossom stems and young 



