Abstract
1. The critical period of determination of future wing development of the apple grain aphid, Rhopalosiphum prunifoliae was determined experimentally at a constant temperature of 25°C, using high population density and starvation as the stimuli.
2. The action of starvation is in general far stronger stimulus for wing development than that of high population density.
3. In the larvae maintained at high population density during 40 hours following the birth or during the earliest stage of the second instar, the percentage values of the winged individuals produced in the third instar are very much larger than those in low density at the corresponding stage.
4. In the larvae forcibly removed from the food plant for 5 to 15 hours immediately following birth and after various hours from 5 to 35 hours following the emergence, high percentages of wing development are always obtained.
5. Maximum rate of wing development caused by the effect of 5 hour starvation is obtained in larvae of 21 hours old which correspond to a later stage of the first instar. And the percentage values greater than 50% are produced during the period extending from 14.5th to 27.5th hour after birth, i.e., from the middle to the end of the first instar.
6. The increase in the rate of wing formation can not be seen in the larvae starved at ages beyond the 10th hour of the second instar.
7. The increase in the rate of wing development is not so remarkable, when the starvation occurs in the earliest stage of larval development.
