Host utilization by Exorista thula Wood (sp. nov.) and Chetogena gelida (Coquillett) (Diptera: Tachinidae), parasitoids of arctic Gynaephora species (Lepidoptera: Lymantriidae)

Abstract

Studies of host-parasitoid interactions undertaken at Alexandra Fiord, Ellesmere Island, Canada, during the summers of 1994, 1995, and 1996 revealed only two species of tachinid flies parasitic on arctic Gynaephora species. Exorista thula sp. nov. (described herein by D.M. Wood) is from the North American Arctic and is parasitic on Gynaephora groenlandica. Remarks on the systematics of Exorista subgenus Exorista in North America and an identification key for arctic and subarctic species of the tribe Exoristini are included. Chetogena gelida, parasitic on Gynaephora rossii, and E. thula were found to be extremely host specific. Both species of parasitoids developed predominantly on final-instar larvae of their respective hosts, but E. thula also emerged from the penultimate instar (9% of E. thula adults, 19% of hosts) and occasionally from the pupal stage (4% of E. thula adults, 3% of hosts) of G. groenlandica.