Biological control of Drosophila suzukii: Efficacy of parasitoids, entomopathogenic fungi, nematodes and deterrents of oviposition in laboratory assays

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is an invasive pest, originating from South Eastern Asia, which has recently spread to North and South America, Europe, and Morocco in North Africa. This pest causes damage to fruit in the immediate pre-harvest period, thus making insecticide application challenging. In this study, the efficacy of several biological control agents against D. suzukii was evaluated under laboratory conditions. Moreover, three parasitoids species (Pachycrepoideus vindemiae Rondani - Hymenoptera: Pteromalidae, Trichopria drosophilae Perkins - Hymenoptera: Diapriidae, and Leptopilina heterotoma Thomson - Hymenoptera: Figitidae) were evaluated in their ability at detecting and parasitizing D. suzukii larvae, using several substrates (blackberry, Rubus fruticocus L., raspberry, Rubus idaeus L., grape, Vitis vinifera L., cherry, Prunus avium L., and artificial medium). In addition, entomopathogenic fungal (EPF) and nematode (EPNs) strains, both commercial and autochthonous, were tested as control agents against larvae, pupae and adults of D. suzukii; a possible negative effect of these bio-control agents on the activity and development of the parasitoid T. drosophilae was also evaluated. Furthermore, harvested grapes were pre-treated with EPF strains to check the effect of this treatment on the capability of inoculated D. suzukii to lay eggs using no-choice and double-choice tests. The effect of fungal strains, potassium silicate and kaolin were determined on insect oviposition. The parasitoids used were able to actively parasitize both larvae and pupae of D. suzukii infesting fruits. Comparably, autochthonous and commercial strains of EPF and EPNs were effective against different life stages of D. suzukii and harmless to T. drosophilae parasitizing D. suzukii pupae. Furthermore, grape berries treated with conidial suspensions of EPF were much less preferred by D. suzukii adults for egg laying. These outcomes, if confirmed in field, may be introduced in future guidelines for the development of effective biological control strategies against D. suzukii involving parasitoids and entomo-pathogenic bio-control agents.