Conidia of Isaria fumosorosea were submitted to three regimes of temperature and moisture to simulate microclimatic conditions which prevail in temperate (43% RH and 28°C to 98% RH and 15°C), subtropical (75% RH and 35°C to 98% RH and 25°C), and arid areas (13% RH and 40°C to 33% RH and 15°C) with daily fluctuating cycles. Germination, conidial viability, and virulence to Spodoptera frugiperda larvae were less affected after 20days exposure under temperate cycling conditions than under arid and subtropical conditions. Exposure of conidia for 20days to constant nocturnal simulated conditions of any tested regime weakly affected conidial persistence, whereas diurnal conditions exerted the most detrimental effects of high temperatures. However, when tested at both 45°C and 50°C at 33% RH for 160h, the persistence of I. fumosorosea conidia was relatively higher than expected. These results emphasize that climatic conditions prevailing in environments and ecological fitness of fungal isolates have to be taken into account for assessing microbial control strategies.