Evaluation of host specificity of Pachycrepoideus vindemmiae, a potential biological control agent for regulation of Drosophila suzukii in Germany

Abstract: The generalist pupal parasitoid Pachycrepoideus vindemmiae (Hymenoptera:
Pteromalidae) is a cosmopolitan parasitoid of several Diptera families and a facultative
hyperparasitoid. It is a species indigenous in Germany and is currently explored for releases in protected cultures against Drosophila suzukii (Diptera: Drosophilidae), a serious invasive pest in stone fruit and berry production. Preliminary field trials have been promising, but P.
vindemmiae has been tested and dismissed as a biological control agent against several dipteran pests. A reoccurring reason for critical estimation was the low host specificity of P. vindemmiae and possible impacts of mass releases on the Diptera fauna and their parasitoid community. However, the information basis of P. vindemmiae hosts and the respective parasitism rates consists of a mixture of reports with different methods (including fruit samplings, baited traps, laboratory studies and revisions of collections) across many countries. To better understand the relevant Diptera host range in Germany, and to estimate possible non-target effects, a systematic literature review and laboratory experiments with naïve P. vindemmiae and pupae of various Diptera families were conducted. The literature review of 215 publications yielded 74 reports of dipteran primary host species from 14 families. In addition, reports of primary host species of Hemiptera and Lepidoptera were found; however, these reports require critical treatment and may be partially a result of misinterpretations. No-choice parasitism experiments with fresh pupae of eight species from seven Diptera families (Calliphoridae, Cecidomyiidae, Drosophilidae, Muscidae, Sarcophagidae, Syrphidae, Tephritidae) confirmed the broad potential host range, however the tested Cecidomyiidae species was not parasitized, despite of reports of parasitism in the family. The results demand for more research in the host choice of the parasitoid when faced with different Diptera host pupae. This will also help to estimate potential negative effects especially on beneficial taxa in D. suzukii-affected horticultural systems.