The population density of B.bassiana was investigated in corn fields after different fungal formulations were used.Dodine-oat medium was used as the most efficient selective medium for monitoring.The fungal spores were collected by the medium from leaves,air and soil,respectively,to undertake the dynamic tracking of the fungal population.It was detected that the fungal population density in different formulations treated fields were obviously higher than that of control field.The most concentrated fungal population appeared in one hour after treatment,the contents of B.bassiana followed the sequence leaves ＞ air ＞ soil.Then,the fungal populations decreased quickly over time on leaves and in soil,especially in leaves,while it was relatively stable in air.B.bassiana suspension emulsion No.2 showed a higher adsorption ability than other formulations and it was potential for enhancing the efficacy.