INSECTS 



summer, the green apple aphis is found principally on 

 young shoots of the apple twigs, and on water sprouts 

 growing in the orchard. 



During the early part of the summer, the rate of pro- 

 duction rapidly increases in the aphid colonies, and in- 

 dividuals of the summer generations sometimes give 

 birth to young a week, after they themselves were born. 

 In the fall, however, the period of growth again is length- 

 ened, and the families drop offin size; until the last females 

 of the season produce each a scant half dozen young, 

 though they may live to a much greater age than do the 

 summer individuals. 



The young summer aphids born as active insects are 

 inclosed at birth in a tight-fitting, seamless, sleeveless, 

 and legless tunic, as are those hatched from the winter 

 eggs. Thus swathed, each emerges, rear end first, from 

 the body of the mother, but is finally held fast by the 

 face when it is nearly free. In this position, the em- 

 bryonic bag splits over the head and contracts over the 

 body of the young aphid to the tip of the abdomen, 

 where it remains as a cap of shriveled membrane until 

 it finally drops off or is pushed away by the feet. The 

 infant, now vigorously kicking, is still held in the ma- 

 ternal grasp, and eventually liberates itself only after 

 some rather violent struggling; but soon after it is free 

 it walks away to find a feeding place among its com- 

 panions on the leaf. The mother is but little concerned 

 with the birth of her child, and she usually continues 

 to feed during its delivery, though she may be somewhat 

 annoyed by its kicking. The average summer female 

 gives birth to two or three young aphids every day. 



The succession of forms in the families is one of the 

 most interesting phases of aphid life. Investigations 

 have shown that the winged individuals are produced 

 principally by wingless forms, and experiments have 

 demonstrated that the occurrence of the winged forms 

 is correlated with changes in the temperature, the food 



[164I 



