Mortality effects of three bacterial pathogens and Beauveria bassiana when topically applied or injected into house flies (Diptera: Muscidae)

Authors: Johnson, Dana; WEEKS, EMMA - University Of Florida; Lovullo, Eric; Shirk, Paul; Geden, Christopher - Chris

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2018
Publication Date: 12/20/2018
Citation: Johnson, D.M., Weeks, E.N., Lovullo, E.D., Shirk, P.D., Geden, C.J. 2018. Mortality effects of three bacterial pathogens and Beauveria bassiana when topically applied or injected into house flies (Diptera: Muscidae). Journal of Medical Entomology. 56(3):774-783. https://doi.org/10.1093/jme/tjy218.
DOI: https://doi.org/10.1093/jme/tjy218

Interpretive Summary: House flies are global pests and disease carriers for humans and animals. High levels of insecticide resistance makes it increasingly difficult to control them. One potential alternative control strategy is to uses disease organisms that are pathogenic to insects but not humans or other vertebrates. In this study, scientists at the USDA-ARS Center for Medical. Agricultural, and Veterinary Entomology (Gainesville, FL) and the University of Florida evaluated three bacterial pathogens (Pseudomonas protegens, Photorhabdus temperata, and Serratia marcescens) and the fungal pathogen Beauveria bassiana against adult flies. The pathogens were tested two ways; by injecting them directly into the fly or by placing them on the fly's surface. The three bacterial pathogens were all highly virulent when injected, and killed the flies within 24 hours. Beauveria took several days to cause mortality. When the same pathogens were applied topically to the flies, B. bassiana killed the flies slowly but was the most effective pathogen because the bacteria lack a mechanism for getting through the thick exoskeleton of the fly. The results suggest that combinations of B. bassiana with a bacterial pathogen could be superior to either pathogen acting alone.

Technical Abstract: The common house fly (Musca domestica, L. [Diptera: Muscidae]) is a global pest of public health and agricultural importance. The efficacy of conventional insecticides has been waning due to increasing insecticide resistance. A potential management tool is entomopathogenic fungus, Beauveria bassiana (strain L90), although time to death is slower than desired by potential users. This research investigated the effectiveness of three gram-negative bacteria (Pseudomonas protegens pf-5, Photorhabdus temperata NC19, and Serratia marcescens DB11) on house fly mortality when topically applied compared to B. bassiana. The pathogen’s virulence was measured by injection into adult female house flies or by topical applications to the fly’s thorax. All bacterial strains were highly virulent after injection with 1x104 colony forming units (cfu), causing mortality of flies within 24 hr. Beauveria bassiana resulted in high mortality, three days post injection at the high dose of 1x104 conidia/µl. The surfactant, CapSil® at 0.5% was used for topical application of pathogens to the thorax of female flies. Mortality due to topical treatments of P. temperata and S. marcescens was low even at the highest dose of 1x106 cfu/µl. Mortality after topical treatments with P. protegens was evident four days after application of 1x106 cfu/µl. Mortality from B. bassiana was low through day four but increased by day five. These results imply that P. protegens holds considerable potential as a biological control agent for incorporation into an integrated management plan against adult house flies.