Seasonal Activity of Entomophthora muscae (Zygomycetes: Entomophthorales) in Musca domestica L (Diptera: Muscidae) with Reference to Temperature and Relative Humidity

The fungus, Entomophthora muscae (Cohn) Fresenius, commonly infects house flies, Musca domestica L., on feedlots and dairies in southeastern Nebraska. During two fly breeding seasons, disease prevalence increased from <1% in May, June, and July to 25 and 77% in August and September, respectively. Effects of relative humidity (RH) and temperature were examined with regard to infectivity and conidial yield of two isolates of E. muscae. House flies were exposed to conidial discharge at 23, 43, 75, and 98% RH. Infection rates of a Nebraska isolate (NE) were 83-94% regardless of relative humidity. Under constant temperature (25°C) the NE isolate produced conidia for 15-21 h, whereas a California isolate (CA) produced conidia for 18-24 h. Temperatures of 10, 20, 30, and 38°C were examined for effects on conidial yield and duration. More conidia were produced at 10 and 20°C for both isolates. The duration of the conidial discharge was temperature dependent. Shortest conidial discharge occurred at 38°C for the NE and CA isolates (9 and 6 h, respectively). Cadaver weight was correlated to spore yield at 20°C for both isolates and at 30°C for the CA isolate. These results suggest that E. muscae strains are suited to unique environmental conditions and may influence natural or induced epizootics.