Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: House flies are pests of humans and their associated animals throughout the world. Traditional methods of fly control relied heavily on chemical insecticides, but flies have become resistant to every new chemical that has been introduced. Alternative biological control approaches include the use of microbial agents that infect and kill flies but are harmless for people and their animals. In this study, scientists at USDA-ARS Center for Medical, Agricultural and Veterinary Entomology (Gainesville FL) and the University of Florida examined the potential of combining one well-known fungal pathogen of insects (Beauveria bassiana) with three bacteria that will kill flies if they can breach the barrier of the insect body wall. The hypothesis was that B. bassiana would penetrate the fly cuticle and that the bacteria would gain entry through the wound. The results indicated that this was not the case, a result that may be due to antagonistic interactions between B. bassiana and the bacteria. One of the tested bacteria, Pseudomonas protegens, was moderately pathogenic on its own, suggesting that this species and its associated toxins warrant further investigation as a fly management tool.

Technical Abstract: In a previous study, we demonstrated that three bacteria species (Serratia marcescens, Photorhabdus temperata, and Pseudomonas protegens) have high and rapid virulence for adult house when injected into the hemocoel but little effect when applied topically. Here we tested the hypothesis that topical application of these species in combination with the entompathogenic fungus Beauveria bassiana would result in high mortality if fungal penetration of the fly cuticle would allow delivery of the bacteria into the fly hemocoel. Bacteria and B. bassiana were tested either at the same time or by sequential application of the two pathogens 48 hours apart. Results indicated that the combination treatments generally did not result in bacteria breaching the defenses of the host cuticle, although there was evidence of additive effects of B. bassiana and P. protegens. A modified Kirby-Bauer assay indicated that P. temperata and P. protegens had inhibitory effects on vegetative growth of B. bassiana. Results with P. protegens were sufficiently encouraging to warrant further investigation of this species and its associated toxins.