In ‘polyphenism’ such as castes in social insects, diverse phenotypes can be produced, based on a single set of genome depending on environmental conditions. Aphids show various morphology and behavior in their sexual and asexual life cycles. For example, they produce winged and wingless individuals, and sometimes produce solder castes in their parthenogenetic generations. However, the developmental mechanisms generating multiple phenotypes, according to the extrinsic factors such as density conditions, remains to be unraveled. On the other hand, aphids are excellent model　materials for studying polyphenism, owing to their parthenogenetic viviparous reproduction producing a large number of clonal individuals.

    In this study, we histologically compared the wing development between winged and wingless lines in two aphid species Acyrthosiphon pisum and Megoura crassicauda. At the first instar stage, the wing primordia were observed in both future winged (WD) and wingless (WL) individuals, which are induced by density manipulations. At the third-instar stage, however, wing buds and flight muscles were well-developed in WD nymphs, while wing primordia were degenerated in WL ones.

    Furthermore, we observed the development of ovaries and inside embryos in the WD/WL nymphs and adults, on the assumption that there should be some trade-offs between dispersal and reproduction. The size of embryos in WD is smaller than those in WL, and the embryonic stages in WD were also lagging those in WL. Interestingly, the comparing of embryos in the same revealed that the stages of WD embryos precede those of WL embryos. This suggests that there is some heterochronic regulation that enables WD adults to rapidly produce offspring after the dispersal flight. Thus, aphids seem to possess the elaborate developmental regulation in relation to dispersal and reproduction, which allows them to accomplish the functions of both phenotypes in the complicated life cycles.