Parasitoid Attack on a Pyramid-Shaped Egg Mass of the Peacock Butterfly, Inachis io geisha (Lepidoptera: Nymphalidae)

Abstract

Females of the peacock butterfly, Inachis io geisha, oviposit their eggs on the undersurface of food plant leaves in a pyramid-shaped mass consisting of several layers. Egg masses deposited on Humulus lupulus were collected from eight sites in southern Nagano Prefecture in Japan, and the variation of egg mass size, parasitoid species and percentage parasitism of each egg mass were examined. Two species of egg parasitoiods, Telenomus sp. and Trichogramma dendrolimi, were found at all collection sites, and the percentage of parasitism of the egg masses varied from 20 to 75% depending on the collection site. The number of eggs per mass varied from ca. 40 to 800. The percentage of surface layer eggs decreased linearly with increases in egg mass size. There were upper limits in the percentage of parasitized eggs among the different egg mass sizes, although the precise relationship between egg mass size and percentage parasitism was not clear. In southern Nagano Prefecture, parasitoid utilization of I. io geisha eggs was not maximized at almost all collection site. In Minamizawa, however, almost all surface layer eggs were parasitized. At such sites, the pyramid-shape of the egg mass of I .io geisha might be expected to afford protection against parasitoid attacks.