Drosophila parasitoids in northern Italy and their potential to attack the exotic pest Drosophila suzukii

Drosophila suzukii is an invasive alien pest recently introduced into Europe and North and South America. Several control methods have been tested, and the ability of natural enemies to control this pest has been investigated. This study aimed to identify the main parasitoids of drosophilids in North Italy via field surveys, and to evaluate the ability of some of those species emerged to parasitize D. suzukii compared to indigenous D. melanogaster. A nine-site survey from July to October 2014 that exposed fruit (banana and blueberry) for 7 and 14 days obtained six parasitoid species, ranked from highest abundance: Leptopilina boulardi, L. heterotoma (Hymenoptera: Figitidae), Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae), Trichopria cf. drosophilae (Hymenoptera: Diapriidae), Asobara tabida (Hymenoptera: Braconidae), and Spalangia erythromera (Hymenoptera: Pteromalidae). The presence and abundance of these species varied greatly among the sites and across the season. The field survey results showed a relationship between parasitoids and indigenous Drosophila communities and a high host competition. The ability of larval parasitoids L. boulardi and L. heterotoma and pupal parasitoid T. cf. drosophilae to parasitize the exotic and indigenous hosts was laboratory tested. Both larval parasitoids failed to develop on D. suzukii, but high mortality was recorded in larvae exposed to L. heterotoma. On the contrary, T. cf. drosophilae developed successfully on D. suzukii, with no significant differences between the exotic and indigenous hosts. These results beg further investigations of indigenous enemies, particularly T. cf. drosophilae, for effective biological control of D. suzukii.