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

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 Novković & Kimura (both Hymenoptera: Figitidae) from Asia are potential agents for classical biological control of the invasive Drosophila suzukii Matsumura (Diptera: Drosophilidae) in North America. We 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 through physiological suppression, with L. japonica out-competing the other two parasitoid species in multi-parasitized hosts. Ganaspis brasiliensis adults discriminated strongly against hosts previously parasitized by L. japonica, and A. japonica adults discriminated against hosts previously parasitized by L. japonica, whereas L. japonica only discriminated against hosts parasitized by G. brasiliensis. Regardless of host density, the observed parasitism when both A. japonica and L. japonica were present was 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.