Plant and host effects on the leafroller parasitoid Dolichogenidia tasmanica

Parasitism by the braconid wasp Dolichogenidia tasmanica of first instar la rvae of the lightbrown apple moth Epiphyas postvittana, established on four different species of potted host plants, was assessed after 2 weeks of fie ld exposure in an apple orchard. Parasitism varied significantly between la rval host plants (apple 58%, broom 59%, clover 30%, poplar 19% ). Parasitis m on potted apple seedlings of the co-evolutionary host, E. postvittana, wa s compared in a field trial with that of two native New Zealand leafroller species (to which D. tasmanica has had exposure for 5 decades only). Parasi tism varied significantly with larval host (E. postvittana, 83%; Ctenopseus tis herana, 58%;Planotortrix octo, 26% ). Larval collections were made from mature apple trees and identification of larvae was achieved by DNA analys is for the leafroller species using PCR-RFLP of ITS1 + ITS2, and for the pa rasitoid by specific PCR of partial 18S. Parasitism under natural field con ditions on mature apple trees was not different between larval hosts (mean 32.5% ). In laboratory studies, more P. octo larvae departed in response to parasitoid probing behaviour than E. postvittana, which is likely to contr ibute to the difference in parasitism rates. This study conclusively shows that D. tasmanica parasitises native New Zealand leafrollers, despite their different evolutionary origins.