Classical biological control, i.e., the introduction of natural enemies from an invasive pest’s area of origin, has been proposed repeatedly to control the spotted wing drosophila Drosophila suzukii in the Americas and in Europe. Results from surveys in Asia and laboratory experiments suggest the parasitoid G1 Ganaspis cf. brasiliensis as a suitable biological control agent. To study the host specificity of the parasitoid under semi-field conditions, we conducted large-arena field cage releases. Parasitoids were released into cages at three dates in August 2021 in two regions of Switzerland. 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). Thus, the results support findings from previous laboratory experiments that G1 G. cf. brasiliensis is highly specific to D. suzukii larvae feeding in fresh fruits and parasitism of the closely related D. melanogaster feeding on decomposing fruits is very rare. Because in its invaded range, D. suzukii is the only Drosophila species that can attack and develop in undamaged fresh fruits, we conclude that open field releases of the parasitoid G1 G. cf. brasiliensis should not pose significant risks to non-targets.

经典的生物防治，即从入侵性害虫的原产地引入天敌，在美洲和欧洲已被反复提出来防治斑点翅果蝇Drosophila suzukii 。亚洲调查和实验室实验的结果表明寄生蜂 G1 Ganaspis cf。brasiliensis作为一种合适的生物防治剂。为了研究寄生蜂在半田间条件下的宿主特异性，我们进行了大竞技场田间笼子释放。2021 年 8 月，在瑞士的两个地区，寄生蜂在三个日期被释放到笼子里。被释放的寄生蜂可以选择寄生于D. suzukii新鲜水果（蓝莓或接骨木）中的幼虫或分解水果的非目标本地物种黑腹果蝇。结果是明确的，以新鲜水果为食的D. suzukii幼虫的明显寄生率平均为 15%，而以腐烂的水果为食的D. melanogaster只有一只寄生蜂（0.02% 的寄生率）。因此，结果支持先前实验室实验的结果，即 G1 G. cf. brasiliensis对以新鲜水果为食的D. suzukii幼虫具有高度特异性，而以腐烂水果为食的密切相关的D. melanogaster的寄生非常罕见。因为在它的入侵范围内，D. suzukii是唯一可以在未受损的新鲜水果中攻击和发育的果蝇物种，我们得出结论，寄生蜂 G1 G的露天释放。brasiliensis不应对非目标造成重大风险。