Abstract: A highly virulent strain of entomopathogenic fungus Beauveria bassiana against aphids was obtained. However, its field application is restricted because aphid reproduction is rapid while B. bassiana infection is relatively slow. To overcome the problem, we conducted a series of bioassay tests against the aphid Lipaphis erysimi, using B. bassiana and three pesticides individually, imidacloprid, dimethoate and beta-cypermethrin at different concentrations, as well as mixtures of the fungus with each pesticide. The results showed that B. bassiana alone at 0.08×10⁶-50×10⁶ spores/mL caused a 47.0%-89.3% mortality rate of the aphids. The mortality was significantly increased to 97.3%~100% by a mixed treatment of 2×10⁶ spores/mL of B. bassiana with a sublethal concentration of each of the three pesticides, i.e., 1/10 of the recommending concentration of imidacloprid, 1/5 of the recommending concentration of dimethoate or beta-cypermethrin. Moreover, the LT₅₀ of mixed treatment was shortened to 46.9-56.5 h from 76.8 h for B. bassiana alone. In addition, the germination rates of B. bassiana conidia mixed with each pesticide were compatible with each other. This experiment confirmed the synergistic effect of B. bassiana with the three pesticides, and determined the appropriate concentration in the mixed application. The data offer a potential opportunity for reducing chemical pesticide use and improving the effect of B. bassiana in aphid management in the field.

Key words: Beauveria bassiana, aphid, imidacloprid, dimethoate, cyhalothrin, synergism