Topical treatment of adult house flies, Musca domestica L. (Diptera: Muscidae), with Beauveria bassiana in combination with three entomopathogenic bacteria

Abstract

Abstract Biological control of house flies, Musca domestica L. (Diptera: Muscidae) has the potential to improve the efficacy and sustainability of integrated pest management. In a previous study, we demonstrated that three bacteria species (Serratia marcescens Bizio [Enterobacteriales: Enterobacteriaceae], Photorhabdus temperata Fischer-Le Saux et al. [Enterobacteriales: Enterobacteriaceae], and Pseudomonas protegens Ramette et al. [Pseudomonadales: Pseudomonadaceae]) are extremely virulent, inducing rapid morbidity and high mortality in adult house flies when injected into the hemocoel but show little effect when applied topically. Here we tested the hypothesis that topical application of these species in combination with the entompathogenic fungus Beauveria bassiana (Bals. Criv.) Vuill. (Hypocreales: Cordycipitaceae) would result in an increased and rapid mortality if fungal penetration of the fly cuticle allowed for increased delivery of the bacteria into the fly hemocoel. Bacteria and B. bassiana were tested either by application at the same time or by sequential application of the two pathogens 48 h apart. Results indicated little evidence for synergy between B. bassiana and any of the bacterial pathogens. However, P. protegens caused early mortality (<50 % at 3 days) when applied alone and in combination with B. bassiana. A modified disc diffusion assay indicated that P. temperata and P. protegens had inhibitory effects on the vegetative growth of B. bassiana suggesting the release of antifungal molecules by the bacteria. Results with P. protegens were sufficiently encouraging to warrant further investigation of this species and its associated toxins as house fly biological control tools.