Classical biological control of the glassy-winged sharpshooter, Homalodisca vitripennis, by the egg parasitoid Gonatocerus ashmeadi in the Society, Marquesas and Austral archipelagos of French Polynesia

Abstract

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (= H. coagulata [Say]) (Hemiptera: Cicadellidae), was a major exotic pest in French Polynesia until a classical biological control program against this pest was conducted using the host-specific egg parasitoid Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae). After risk assessment studies indicated an acceptably low potential threat to non-target species, parasitoids were released on Tahiti in May 2005. One year after release, populations of H. vitripennis had decreased by more than 90% in Tahiti and nearby Moorea. Here we present results of impact studies obtained during the second post-release year for G. ashmeadi in Tahiti and Moorea; we also report for the first time on results for eight other H. vitripennis infested islands located in three different archipelagos (Society, Marquesas, and Austral) of French Polynesia. On all infested islands across the three archipelagos, arrival of G. ashmeadi slashed H. vitripennis densities by more than 95%. In Tahiti and Moorea, H. vitripennis populations were maintained at very low densities during the second post-release year. Seasonal fluctuations of H. vitripennis abundance were observed in Tahiti with pest populations being more abundant during the cooler dry season than during the warmer wet season because of lower parasitism rates. Hence, similar seasonal fluctuations of H. vitripennis abundance are expected across all infested archipelagos in French Polynesia.