Impacts of invasive parasitoids on declining endemic Hawaiian leafroller moths (Omiodes: Crambidae) vary among sites and species

Abstract

Summary 1. Invasive parasitoids and predators, both accidentally and purposefully introduced, have variously altered native insect communities worldwide, sometimes causing major declines and extinctions. Most species of endemic Hawaiian leafroller moth in the genus Omiodes (Lepidoptera: Crambidae) have suffered range reductions and local extirpations and some species appear to be extinct. Non-native parasitoids, particularly those introduced for biological control, have been implicated in declines of non-target Omiodes and other Hawaiian Lepidoptera. 2. We assessed parasitism rates on Omiodes through controlled exposure trials using Omiodes continuatalis, a species once thought to be extinct due to non-native parasitoids. A total of 2514 O. continuatalis larvae were used in exposure trials on the islands of Maui and Oahu in 2006 and 2007. We also conducted extensive surveys for wild larvae of two target and three non-target Omiodes species, the latter also of conservation concern. Over 4 years, we collected 500 wild larvae across four islands to assess parasitoid impacts and compare results between wild larval collections and controlled exposure. 3. Exposure trials estimated parasitism rates of O. continuatalis from 15·6% to 65·3% and field surveys indicated observed parasitism of 8·1–100%, depending upon the species and locality. Accidentally introduced or cryptogenic (of unknown origin) parasitoids were responsible for 85·7% of parasitism in deployed Omiodes larvae and 56·6% of observed parasitism in wild Omiodes larvae surveyed in 2007. 4. The variation in these data appears to be associated with habitat level characteristics, which, in combination with species-specific features, may mediate the impacts of non-native parasitoids on Omiodes species. 5.Synthesis and applications. Biological control agents may not be a primary cause of decline or extinction for some native moths. Successful conservation planning for threatened and declining insects will benefit from consideration of the synergistic effects of parasitoids and habitat on a species by species basis.