Page:Insects - Their Ways and Means of Living.djvu/200



summer, the green apple aphis is round principally on young shoots of the apple twigs, and on water sprouts growmg in the orchard. During the early part of the summer, the rate of pro- duction rapidly increases in the ap.hid colonies, and in- dividuals of the summer generatons 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 hall dozen young, though they may live to a much greater age than do the sunamer 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 ena- 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; btt soon after if is free it walks away to find a feeding place anaong its com- panions on the leaf. The mother is but little concerned with the birth of her child, and she usually continues to feed dtring its delivery, though she may be somewhat annoved by its kicking. The average summer female gives birth to two or three young aphids every day. The succession of forms in the familles is one of the most interesting phases of aphid lire. 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

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