Potential for the classical biological control of Drosophila suzukii using the parasitoid Ganaspis brasiliensis
Drosophila suzukii (Diptera: Tephritidae – EPPO A2) is a frugivorous fly native to East Asia. It has spread to many regions worldwide, including other parts of Asia, the Americas, Africa and the EPPO region. Surveys have been conducted in the native range of the pest to explore natural enemies that could be used as classical biological control agents in the introduced, invasive range. A parasitoid Ganaspis brasiliensis (Hymenoptera: Figitidae) is the most specific natural enemy of D. suzukii, though host specificity varies between different G. brasiliensis populations. In laboratory experiments, one particular genetic group, G1 G. cf. brasiliensis almost exclusively parasitized Drosophila spp. larvae feeding on ripening fruits. In invaded areas, D. suzukii is the only drosophilid that can lay eggs in fresh fruits, the ecological host range of G1 G. cf. brasiliensis is very likely to be restricted to this species. In Switzerland, based on the host range results in the laboratory, experimental field cage releases were approved by the Swiss government in June 2021. The aim of these caged releases was to (1) to test releases of a parasitoid into large-arena field cages as a method for confirming its host specificity under semi-field conditions, and (2) to verify the host specificity of G1 G. cf. brasiliensis to Drosophila spp. in fresh fruits under more natural conditions.Released parasitoids had the choice to parasitize either D. suzukii larvae in fresh fruits (blueberries or elderberries) or the non-target native species D. melanogaster in decomposing fruits. The results were unequivocal in that apparent parasitism of D. suzukii larvae feeding in fresh fruits was on average 15%, whereas only one parasitoid emerged from D. melanogaster feeding on decomposing fruits (0.02% parasitism). The authors conclude that open field releases should not pose significant risks to non-target organisms.
Sources
Seehausen ML, Valenti R, Fontes J, Meier M, Marazzi C, Mazzi D, Kenis M (2022) Large-arena field cage releases of a candidate classical biological control agent for spotted wing drosophila suggest low risk to non-target species. Journal of Pest Science. https://doi.org/10.1007/s10340-022-01487-3