Abstract: [Objective] In this study, ultraviolet irradiation was used to mutate Beauveria bassiana BH01, isolated from an infested larvae of Hyphantria cunea (Drury) (Lepidoptera:Arctiidae), to select high virulent mutants and provide new engineered strains for the biocontrol of H. cunea.[Method] The spore suspension of BH01 was put under UV lamp to mutagenize, positive mutant strain was first selected based on the mutation strains' spore yield which was more than 2 times of original strains. Then the pathogenicity of positive mutant strains to 5^th instar larvae of H. cunea was determined. The screened high virulent mutant strains were subculture to determine the stability of the sporulation yield and pathogenicity.[Result] We obtained 28 colonies after UV treatment, and the corrected mortality of spore was 85.5%. The colonies acquired after UV treatment were cultured on PDA plate and three positive mutant strains of BH01-5, BH01-12, and BH01-25 with more than 2 times higher spore yield than the original strain were obtained. Contrast to the original strains, the corrected mortality of 5^th instar larvae of H. cunea caused by the mutant strain BH01-5 was significantly lower, and BH01-25 caused the almost equivalent mortality. However, the BH01-12 caused the significantly higher mortality, and the corrected mortality and LT₅₀ values were 1.30 and 0.68 times higher than that of the original strain, respectively, and the differences are statistically significant. The mutant strains BH01-12 and BH01-25 were subcultured 6 generations. The results showed that the spore yield and pathogenicity of BH01-25 decreased gradually, with the same trend with the original strain. But the spore yield was always higher than that of the original strain. In addition, the pathogenicity of original strain decreased from the 4 generation, while that of BH01-25 decreased from the 6 generation, indicating the better stability of the mutant. In contrast, both the amount of spore production and the pathogenicity to the larvae of H. cunea of the mutant strain BH01-12 were not declined during the 6 generation of subculture, indicating the mutant was significantly better than that of original strain.[Conclusion] After the UV mutagenizing to B. bassiana BH01 isolated from diseased larvae of H. cunea, a mutant strain BH01-12 with higher spore yield and pathogenicity was obtained. During 6 generation sub-culture of the mutant, the spore production and pathogenicity of BH01-12 had no any reduction, showing to a certain degree genetic stability and good production and application prospects.

Key words: Beauveria bassiana, UV mutagenizing, sporulation yield, pathogenicity, Hyphantria cunea (Drury)