Potential competitive outcomes among three solitary larval endoparasitoids as candidate agents for classical biological control of Drosophila suzukii

Authors: Wang, Xingeng; Hogg, Brian; HOUGARDY, EVELYNE - University Of California; NANCE, ALEXANDRA - University Of California; DAANE, KENT - University Of California

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2018
Publication Date: 12/12/2018
Citation: Wang, X., Hogg, B.N., Hougardy, E., Nance, A., Daane, K.M. 2018. Potential competitive outcomes among three solitary larval endoparasitoids as candidate agents for classical biological control of Drosophila suzukii. Biological Control. 130:18-26. https://doi.org/10.1016/j.biocontrol.2018.12.003.
DOI: https://doi.org/10.1016/j.biocontrol.2018.12.003

Interpretive Summary: Spotted wing drosophila invaded California in 2008 and has since become one of the most damaging pests of soft-skinned fruit such as strawberries, blueberries and cherries. Its ability to attack ripe fruit makes it particularly damaging. Three parasitic wasps that attack spotted wing drosophila larvae were collected from its native range in Asia and are under consideration for release in California to help control this pest. Once released these wasps are likely to interact, and may interfere with each other, or they may work together to increase control of spotted wing drosophila. Individual spotted wing drosophila larvae may be parasitized by more than one wasp species at a time. In this study we compared the competitive abilities of these wasps and tested whether competition between them compromises or enhances spotted wing drosophila control. One wasp had a competitive advantage over the other two because its eggs hatched fastest. Our results showed that this wasp eliminated the other two species soon after egg hatching, most likely through physical combat. One of the other wasps only attacked spotted wing drosophila larvae that were not previously parasitized by the fast-developing wasp. Numbers of parasitized larvae were higher when these two wasps were together, and spotted wing drosophila control increased. However, the third wasp did attack larvae that were parasitized by the fast-developing wasp, and was eliminated when the fast-developing wasp was present. Thus, these two wasps interfered with each other, and spotted wing drosophila control decreased when they were together. These results suggest that releasing the two wasps that worked effectively together may be the best strategy for increasing spotted wing drosophila control.

Technical Abstract: Predicting the outcome of interspecific interactions is important in designing biological control programs that involve multiple species introductions. Three solitary larval endoparasitoids, Asobara japonica Belokobylskij (Hymenoptera: Braconidae), Ganaspis brasiliensis Ihering and Leptopilina japonica Novkovic & Kimura (both Hymenoptera: Figitidae) from Asia are potential agents for classical biological control of the invasive Drosophila suzukii Matsumura (Diptera: Drosophilidae) in North America. This study first compared the developmental rates of early immature stages of the three parasitoids and then evaluated their potential interactions, including elimination of competitors in intrinsic competition, interspecific discrimination of previously parasitized hosts, and the outcomes of interspecific competition at three host densities (5, 15 or 30 host larvae). On average, L. japonica eggs hatched first, followed by A. japonica and then G. brasiliensis. All three species exhibited interspecific competition after egg hatch through physical combat or in some cases physiological suppression, with L. japonica out-competing the other two parasitoid species in multi-parasitized hosts. G. brasiliensis adults discriminated strongly against hosts previously parasitized by L. japonica, and A. japonica adults discriminated against hosts previously parasitized by L. japonica, but L. japonica did not discriminate against hosts parasitized by A. japonica. Regardless of host density, the observed parasitism when both A. japonica and L. japonica were present was always lower than expected, a likely consequence of interspecific competition, but the combined impacts on host suppression by L. japonica and G. brasiliensis were additive, likely due to strong interspecific discrimination by G. brasiliensis.