Biocontrol potential of entomopathogenic nematodes and entomopathogenic fungi against the soil-dwelling stages of spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae)

Spotted-wing drosophila (SWD), Drosophila suzukii, is an invasive pest of small fruits such as blueberries and raspberries, causing substantial yield losses. This study evaluated the biocontrol potential of entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPF) against the last instar larvae and pupae of D. suzukii. In the first experiment, three EPN species, Steinernema carpocapsae (ALL strain), S. feltiae (SN strain), and Heterorhabditis bacteriophora (SN strain), were applied at a rate of 50 infective juveniles (IJs) cm⁻2. S. feltiae was the most effective, reducing adult D. suzukii emergence to 20 % from larvae and 40 % from pupae. A subsequent experiment tested nine EPN species, including S. carpocapsae, S. riobrave (355 strain), S. glaseri (VS strain), H. indica (HOM1 strain), H. georgiana, H. floridensis, and H. megidis (UK211 strain). Among these, S. feltiae, S. carpocapsae, and S. glaseri consistently reduced adult emergence to below 50 %, with S. feltiae achieving 20 % emergence at 100 IJs cm⁻2. In a third experiment, three EPF, Beauveria bassiana, Metarhizium brunneum, and Cordyceps fumosorosae, were evaluated. B. bassiana proved most effective, reducing D. suzukii adult emergence by more than 50 % at 1 × 108 conidia mL⁻1. In the final experiment, combinations of S. carpocapsae, S. feltiae, or S. glaseri with B. bassiana at both 50 and 100 IJs cm⁻2 further reduced emergence, with the most effective treatment resulting in only 8 % adult emergence. These findings demonstrate the strong potential of EPNs and EPF, individually and in combination, as biocontrol agents targeting the soil-dwelling stages of D. suzukii.