206 MAINE AGRICULTURAL EXPERIMENT STATION. IQIS- 



LIFE HISTORY. 



The pink and green aphid of potato is found in the spring 

 upon rose bushes, feeding on the succulent growth and especially 

 abundant near the flower buds. Unlike many species of plant- 

 lice, migration with this insect may occur through wingless as 

 well as winged individuals. The winged ones take flight, and 

 the others, if they are near enough, walk over to potato plants. 

 This occurs in Maine ordinarily from the first to the middle of 

 July, when a very few scattered individuals may be seen upon 

 the potato. Upon this plant they seem to find conditions ideal 

 for growth and increase enormously, often before the last of 

 August covering the tender tips and blossom stalks thickly with 

 their colonies. At this time a single female may produce more 

 than 50 young in 2 weeks, and it takes, in warm weather, about 

 2 weeks after birth for a female of this species to attain maturity 

 and begin to produce young. A glance at figure 48 will show 

 the result of a heavy infestation of 14 days duration upon the 

 potato plant. 



By the middle of September the fall migration is over and 

 the aphids have deserted the potato fields. The indoor studies 

 with this insect indicate that when it leaves the potato it pre- 

 fers the rose, but will colonize upon a variety of plants, part of 

 which are common weeds. This seems more like a dispersal 

 from the potato than a "return migration" in the sense this 

 term is used with reference to those aphids which accept only 

 two kinds of food plant — the first for the fall, the overwinter- 

 ing egg and the spring, and the second for the summer months. 

 However, the rose seems to be the favorite and it is probable in 

 Maine that this serves most commonly for the fall generations 

 of the potato aphid. The last generation of the year consists in 

 the wingless, egg-laying females and the winged males, — or the 

 so-called "true sexes" which appear in Maine about September 

 20 and only at this one time, all the other generations consisting 

 entirely of viviparous females. The insectary observations of 

 1907 showed that under indoor conditions, the true sexes may 

 be produced and the overwintering eggs may be deposited on 

 both potato and shepherd's purse. It is likely that this gen- 

 eration can be produced on other accepted food plants also. No 

 evidence has been found in the field, however, that the true 

 sexes or eggs occur normally upon the potato, for the aphids 



