Engineering an invasion: classical biological control of the glassy-winged sharpshooter, Homalodisca vitripennis, by the egg parasitoid Gonatocerus ashmeadi in Tahiti and Moorea, French Polynesia

Abstract

The glassy-winged sharpshooter, Homalodisca vitripennis Germar (=H. coagulata Say) (Hemiptera: Cicadellidae), invaded Tahiti in 1999 and spread rapidly to the main island groups of French Polynesia becoming an important pest. It threatened agriculture, native biodiversity, and created serious social and recreational problems. Further, massive uncontrolled populations on Tahiti presented an elevated invasion threat to other South Pacific nations. In 2004, a classical biological control program against H. vitripennis was initiated in French Polynesia using the highly host-specific egg parasitoid Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae). After risk assessment studies indicated an acceptably low level of risk to non-target species, 13,786 parasitoids were released at 27 sites in Tahiti between May and October 2005. Here we present the results of G. ashmeadi and H. vitripennis population surveys during the first year of their interaction in French Polynesia (until mid-May 2006). The impact of G. ashmeadi on H. vitripennis was extremely rapid and high. Parasitism of H. vitripennis egg masses by G. ashmeadi has averaged 80–100% in Tahiti since the introduction of the parasitoid, and populations of H. vitripennis nymphs and adults have decreased by more than 90% since December 2005. Populations of H. vitripennis have been successfully maintained at this low level for more than 1 year. The same results were obtained in nearby Moorea where the parasitoid was probably spread by the unregulated transport of plants infested with parasitized H. vitripennis eggs. Population monitoring continues in order to determine if a stable equilibrium between the pest and the parasitoid has been reached.