Individual and combined effects of larval and pupal parasitoids in the control of <i>Drosophila suzukii</i> (Diptera: Drosophilidae): implications for biological control

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a major pest of soft-skinned fruits, with its strong reproductive capacity and adaptability rendering chemical control methods ineffective and environmentally risky. Biological control using parasitoid wasps is a sustainable alternative. This study focused on the larval parasitoid Leptopilina japonica Novković & Kimura (Hymenoptera: Figitidae) and 2 pupal parasitoids, Trichopria drosophilae Perkins (Hymenoptera: Diapriidae) and Pachycrepoideus vindemmiae Rondani (Hymenoptera: Pteromalidae), to evaluate their individual and combined effects on the control of D. suzukii. Experiments were conducted across a range of host densities (5 to 30 individuals per blueberry fruit) and different host patch types (within blueberries or as exposed pupae). The study measured offspring production, host stinging without oviposition-induced mortality, and total host mortality caused by the parasitoids. The implications for biological control of D. suzukii were also evaluated. The results showed that the parasitic efficiency of all 3 parasitoid species increased with host density, but L. japonica caused significantly higher mortality at high densities (≥20 hosts) compared to the pupal parasitoids. Trichopria drosophilae and P. vindemmiae exhibited stable performance in pupal parasitism, with P. vindemmiae showing stronger adaptability to concealed hosts. Population suppression experiments demonstrated that the combined release of L. japonica and T. drosophilae achieved the optimal control effect, significantly reducing the number of D. suzukii adults after 45 d compared to the control group, while also promoting significant population growth of the parasitoids. This study demonstrates that the combined release of larval and pupal parasitoids can significantly enhance control efficiency against D. suzukii.