Non-target host risk assessment for the parasitoid Torymus sinensis

Abstract

Torymus sinensis Kamijo (Hymenoptera: Torymidae) has been released throughout Italy for biological control of the chestnut gall wasp. In response to concern about non-target impacts associated with the introduction of this exotic biological control agent, this study aimed at investigating T. sinensis’s host range. In total, 1371 non-target galls were collected in north-central Italy in a two-year period, representing nine different species. Collections were carried out on common oak, downy oak, sessile oak, Turkey oak, and wild rose. A total of five native torymid species were recorded from the non-target galls (Megastigmus dorsalis, Torymus affinis, T. auratus, T. flavipes, and T. geranii), and three ♂♂ T. sinensis individuals emerged from Biorhiza pallida galls collected in the field. Under controlled conditions, most of the non-target galls tested were not suitable hosts for oviposition. T. sinensis females only laid eggs on Andricus curvator. In olfactometer bioassays, higher numbers of T. sinensis females showed more interest to the chestnut galls compared to non-target hosts. This data highlights how T. sinensis has a broader ecological host range than reported in the literature and that it is attracted by non-target hosts other than D. kuriphilus.