Behavioral Fever Response of Musca domestica (Diptera: Muscidae) to Infection by Entomophthora muscae (Zygomycetes: Entomophthorales)

House flies, Musca domestica L., infected with Entomophthora muscae (Cohn) Fresenius were exposed to 40°C to determine the effects of high temperature on diseased house flies. In no-choice experiments, high temperatures early in the incubation period of two isolates of E. muscae increased the survival time of diseased house flies. House flies surviving E. muscae infections induced by a Nebraska/NE) isolate were 87, 78, and 37% if exposed to high temperature for 8 hr during Days 1, 2, and 3 of the incubation period, respectively. House fly survival rates declined to 17 and 13% if exposed to high temperature on Days ,4 and 5 of the usual 5-day incubation period. House flies surviving infections induced by a California (CA) isolate were 93, 97, and 92% if exposed to 40°C temperatures for 8 hr during Days 1, 2, and 3 of the incubation period. Survival rates declined to 75, 38, and 17% if high temperature exposures occurred on Days 4, 5, and 6 of the typical 7-day incubation period. Short-term exposures (4-6 hr) of E. muscae (NE) infected house flies (24 hr old) to 40°C increased fly survival 90%. Similar results were not observed at 35°C. In free-choice experiments, house flies infected with the NE isolate of E. muscae for 24-48 hr exhibited a behavioral fever and were able to use heat therapy to eliminate pathogenic effects of E. muscae. The response was not consistent throughout the E. muscae incubation period. Behavioral fevers were not exhibited by infected house flies on Days 1, 4, and 5 of the incubation period. On Day 5 of the incubation period, dying flies moved to the cool regions of the gradient.