Comparison of the Effects of Pesticide Application on Biston suppressaria Larvae in Different Damage Stages

[Objective] The paper was to determine the optimal control period of Biston suppressaria, the most serious defoliator in eucalyptus forests in southern Fujian Province. [Method] By spraying 2% abamectin + Bacilus thuringiensis powder in the forest, the first generation larvae of B. suppressaria was controlled in the early damage stage(May 2), middle damage stage(May 13) and late damage stage(May 30), respectively.[Result] When 500 g of pesticide was sprayed per 667 m^(2) in the early damage stage of the first generation larvae, the population reduction rate was97.5 % at 5 d post spraying. When 500 g of pesticide was sprayed per 667 m^(2) in the middle damage stage, the population reduction rate was 95.3% at 5 d post spraying. When 1 000 g of pesticide was sprayed per 667 m^(2) in the late damage stage, the population reduction rate was 83.9%, conspicuously lower than those in the early and middle damage stage. If pesticides were sprayed in the early and middle damage stage, the second gen-eration larvae would not cause harms, but the second generation larvae would cause slight harms if pesticides were sprayed in the late damage stage.[Conclusion] Control before the middle damage stage has significant effect on improving the control effect and reducing losses while reducing the usage of pesticides.