Effects of population density on alienicolae of Aphis fabae Scop. I. The effect of crowding on the production of alatae in the laboratory.

SUMMARY A wide range of morphological differences, from apterae to alatae, and of differences in the behaviour of alatae were produced by isolating alatiform nymphs of Aphis fabae on successive days after their birth. Alatiform. nymphs isolated soon after birth developed into the extreme apterous form, whereas when kept in a crowd until shortly before their final ecdysis a large proportion became alatae that flew before depositing young (migrants). Alatiform nymphs isolated on successive days after birth developed either into alatae that flew after depositing nymphs (flyers) or did not fly (non-flyers). Aphids thus show a continuous polymorphism, comparable to that of locusts, and possibly related to concentrations of juvenile hormone present in the aphid during larval development.

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