Abstract: Temperature and relative humidity pose great effects on the virulence of entomopathogenic fungi. The objective of this study was to examine the effect of interacting conditions of temperature and relative humidity on fungal infection of Beauveria bassiana towards Stephanitis nashi and Locusta migratoria manilensis. The insects were inoculated with conidia suspension of B. bassiana at a concentration of 1.0×10⁷ spores/mL and were fed and held at 25℃. It was observed that the fungal virulence increased with the increase of relative humidity. To describe mortality dynamic of the tested insects, a model of time-humidity-mortality (THM), derived from the model of the time-dose-mortality (TDM), was established. Development of the fungal disease could be well described by the THM model with the change of humidity and time variables. The THM model showed that, when humidity was over 85%, the mortality of S. nashi was significantly higher than that of L. migratoria manilensis. By comparison of the mortalities in different days, the time parameters γ maximized on the 8th day for S. nashi and on the 11th day for L. migratoria manilensis, indicating that S. nashi is more sensitive to the change of relative humidity than L. migratoria manilensis. As to temperature effects, when relative humidity was over 95%, the fungal infection on both the tested insects peaked at 25℃. Temperature effects on the insects' mortality could not be described by the TDM model but could be fitted well with a logistic model. The model results indicate that S. nashi is easier to be infected than L. migratoria manilensis as evidenced by a faster infection speed and a shorter infection period. The construction of the THM and logistic models is a good way to understand the effects of relative humidity and temperature on fungal infection towards different target insects.

Key words: Stephanitis nashi, Locusta migratoria manilensis, Beauveria bassiana, THM model, Logistic model