Geographical variation in parasitoid communities and the cause of enemy-free space in a range-expanding myrmecophilous lycaenid butterfly

Abstract

Range expansions of host species are likely to modify host–parasitoid interactions. Observational studies have indicated that host species in recently colonized areas are less frequently attacked by parasitoids; however, these studies did not determine whether traditional parasitoids can still use host populations in these areas. Thus, it is unclear why the host has escaped from their traditional parasitoids in their recently colonized areas. In this study, we examined the interaction between myrmecophilous lycaenid butterfly, Arhopala japonica, and its larval parasitoids in northern Japan, a recently colonised area. This region corresponds to a distribution of A. japonica, a myrmecophilous lycaenid butterfly. No parasitoids emerged from A. japonica larvae collected in the north, whereas six parasitoid species attacked the host larvae in native areas. Attacks from the braconid wasp Cotesia sp. near inducta were the most common; however, parasitism tests revealed that Cotesia sp. near inducta and other parasitoid species completed their development successfully regardless of origin of their butterfly hosts. Population genetic analyses supported the recent range expansion of both A. japonica and Cotesia sp. near inducta. These results suggest that both hosts and parasitoids have experienced recent population expansion; however, the more rapid range expansion of A. japonica has caused escape from the enemy in newly colonized areas.