SEASONAL FLUCTUATIONS OF EGG DENSITY AND SURVIVAL RATE IN JAPANESE BLACK SWALLOWTAIL BUTTERFLIES

Abstract

Seasonal fluctuations of eggs and their survival in black swallowtail butterflies in comparison with yellow swallowtail butterflies, i.e. Papilio xuthus and P. machaon, were investigated at a deforested area in Chiba, Kanto district, and at patches of forest gaps in Kochi, Shikoku Island. The black swallowtail butterflies (P. helenus, P. bianor and P. protenor) in Chiba laid eggs on a host tree, Zanthoxylum ailanthoides, in two discrete generations. In Kochi, oviposition by P. helenus and P. protenor also takes place continuously on the same host species throughout the season, i.e. from April to October. The egg density was higher in summer-autumn generation than that in spring one in both localities. Annual variation in the shape of survivorship curves was smaller in the black swallowtail butterflies as compared with that of P. xuthus. The generation mortality from egg to pupa in the summer-autumn generation was lower than that in the spring generation. It was also lower than those of P. xuthus and P. machaon in the comparable generation. The habitat preference of the black swallowtail butterflies was also discussed in comparison with P. xuthus and P. machaon.