Abstract: The entomogenous fungus Aschersonia aleyrodis is a promising whitefly and scale insect control agent. Six widely used pesticides were assessed at the recommended concentrations for compatibility in vitro with A. aleyrodis. The effects of these pesticides on spore germination during the whole test periods (12, 15, 18, 21 and 24 h) and mycelial growth after 5 days of incubation at 25℃ were quantified. Generally, fenpropathrin and propargite had pronounced adverse effects on the fungus. These two pesticides either heavily impaired the development of the fungus or strongly inhibited its spore germination at 25℃ and resulted in fungistasis，which indicated that they were mostly incompatible. Imidacloprid, isocarbophos and amitraz had a stimulating effect on spore germination and the latter two showed a reversible inhibitory effect on the growth of fungus in the tests. However, carbendazim conducted a temporary stimulatory performance on spore germination but performed an inhibitory influence on hyphal development.