Seasonal cycles of Myiopharus aberrans and M. doryphorae (Diptera: Tachinidae) parasitizing Colorado potato beetles in upstate New York

Abstract

Abstract Leptinotarsa decemlineata larvae in potato fields were parasitized by two species of Myiopharus: M. aberrans and M. doryphorae . In both species, males eclosed about 1 day earlier than females, and adult flies were active in July, August, and early September. M. doryphorae appeared to parasitize second-, third-, and fourth-instar larvae, and the parasitoid adults emerged from dead fourth-instar hosts. There were two or more generations per year; however, most parasitism occurred late in the season after a large proportion of the host population had entered diapause and dug into the soil. M. doryphorae's overwintering stage is unknown; this is a significant handicap in using this species in biological control. Unlike M. doryphorae , M. aberrans ' females parasitized only fourth-instar larvae, and its developmental time was approximately 2 days longer than that of M. doryphorae . M. aberrans ' life cycle also appeared to follow closely that of its host. Maggots that were larviposited early in July completed development and adults eclosed from fourth-instar hosts after they dug into the soil. Those that were larviposited late in the season entered an estival-autumnal-hibernal diapause, overwintered, and emerged from the adult beetles during the following spring. Moist soil conditions increased the incidence of successful emergence of M. aberrans from these beetles. Field populations of M. aberrans could be conserved and enhanced by habitat manipulation during spring and summer.