Cleptoparasitic Life of the Tachinid Fly, Symmorphomyia katayamai MESNIL et SHIMA, in the Nest of Host Wasps Hunting the Chrysomelid-larva Prey

Previous knowledge about the tachinid cleptoparasite, Symmorphomyia katayamai MESNIL et SHIMA (Diptera, Tachinidae), a specific attacker on the chrysomelid-larva hunter, Symmorphus spp. (Hymenoptera, Eumenidae), was corrected by observing (1) the activities of host wasps and other insects at nesting sites and colonies of the chrysomelid prey, (2) the developmental process of the tachinid larva, and by inspecting (3) the cell contents of the host nests. No visits by S. katayamai to the host wasp's nesting sites were observed, in spite of the remarkably high percentage of cleptoparasitism on the wasp's nests. It was confirmed that the larva of S. katayamai first has the endoparasitoidal stage on any one of chrysomelid larvae stored in the nest cell. Two puparia of presumably S. katayamai were obtained through rearing chrysomelid larvae collected on the host plant that a female fly had visited. The female reproductive organs of S. katayamai had the structure typical to the ovoviviparous tachinine flies which produce numerous first-instar larvae. A cleptoparasitic life style of S. katayamai is probably derived from the fundamental one of the endoparasitoid on chrysomelid larvae by the phoresy-like access into the nests of Symmorphus wasps.