Some like it hot and some like it hotter - Flies, fever and fungal biopesticides

Intense use of chemical insecticides against the house fly, Musca domestica L. (Diptera: Muscidae) in livestock and poultry operations has resulted in the rapid proliferation of resistant populations, prompting the search for novel methods of control. Spore formulations of the entomopathogenic fungus Beauveria bassiana have been suggested as a possible alternative to chemical insecticides due to their unique mode of action, ease of production and minimal environmental impact. However, house flies are known to reduce the virulent effects of naturally acquired fungal infections by invoking a behavioral fever, with benefits ranging from extended survival to complete clearance of the infection. Here we report on a study investigating the nature and consequences of behavioral fever in the house fly in response to infection with B. bassiana. Flies were infected with the pathogen and behavior and survival compared under constant temperature conditions vs. conditions allowing active thermoregulation. We found that infected flies preferred higher temperatures and allocated more time to thermoregulation than uninfected flies, with the pattern of fever varying with different fungal challenges. This altered thermal behavior allowed infected flies to significantly extend their survival and increase reproductive output relative to flies maintained under constant conditions. The results of this study confirm the adaptive value of fever and highlight the importance of understanding the interaction between host behavior and the environment when integrating biological control agents into pest management practices.