Temperature and moisture relations for conidial sporulation and germination ofEntomophaga maimaiga, an Asian fungal pathogen of gypsy moth,Lymantria dispar(L.), were studied in the laboratory. Germination and sporulation occurred between 2 and 25°C with maximal rates between 20 and 25°C. In 50% of cadavers incubated at 20°C, sporulation began within 17.0 h of the hosts' deaths. Spore production and release readily occurred at 95–100% RH, but only limited spore production was seen at 70% RH, and very few spores were produced or released at 50% RH. Germination was delayed by constant light compared with a rapid response under dark conditions: at 20°C, 50% germination occurred in 3.4 h in the dark, but 9.0 h were required in the light. Conidia required free water for germination. Conidiophores did not develop with constant exposure to 30°C. Conidia could survive relatively short exposures to 30°C;>85% of conidia survived ≤6 h of exposure to 30°C.E. maimaigaprotoplasts inside infected insects were more resistant to higher temperatures:E. maimaigacompleted development in 30% of cadavers despite an exposure period of 48 h at 30°C.