Parasitism and over-wintering status of tachinids (Diptera) on larvae of the fall webworm, Hyphantria cunea Drury (Lepidoptera: Arctiidae), in the Kanto Region of Japan

Abstract

I investigated seasonal changes in the levels of parasitism and the over-wintering status of tachinids on the larvae of Hyphantria cunea. Six species of tachinids were found to parasitize populations of H. cunea at Tsukuba, in central Japan. The rate of parasitism by tachinids was extremely high in the third host generation, especially during the wandering stage. The parasitization rate by the three dominant species, Exorista japonica, Drino inconspicuoides and Compsilura concinnata, was always higher in the wandering larvae than in the feeding larvae. The over-wintering strategy of tachinids differed between species; C. concinnata over-winters at the maggot stage and E. japonica at the early instar maggot and puparial stages. In E. japonica, the rate of over-wintering survival differed greatly between the two over-wintering strategies; individuals over-wintering at the maggot stage within hosts almost all succeeded in adult eclosion in the next year, whereas those over-wintering at the puparial stage out of hosts often died early in the next spring. Many E. japonica maggots over-wintered within hosts collected in late October, suggesting that parasitizing host larvae in late autumn is advantageous for E. japonica. This study provides evidence of different parasitic strategies in tachinid species that use H. cunea as a host.