中文摘要：

以筛选得到的分离自松墨天牛的球孢白僵菌高毒力菌株B5、Bxs、低毒力菌株B11和分离自松毛虫的球孢白僵菌低毒力菌株BZ为出发菌株,记为B0。通过连续接种松墨天牛幼虫分别获得H1、H2、H3、H4;连续在PPDA培养基上继代移殖,分别获得R1、R2、R3和R4,对各原始菌株与继代移殖菌株分别进行毒力测定。结果表明：高毒力菌株B5、Bxs与低毒力菌株B11、BZ在PPDA培养基上继代移殖,各菌株毒力均逐代下降,原始菌株、各继代移殖菌株彼此间的LT50差异显著。分离自松墨天牛的B5、Bxs、B11菌株通过松墨天牛幼虫继代移殖后毒力逐代提高,逐代之间的LT50差异显著;但来源于松毛虫的Bz菌株逐代之间的LT50差异不显著,这可能跟球孢白僵菌对寄主的专化性有关。

英文摘要：

Two strains B5 and Bxs with high toxicity and two strains B11 and BZ with low toxicity to Monochamus alternatus were screened from 15 strains of Beauveria bassiana.Among these,B5,Bxs and B11 were isolated from M.alternatus,BZ was isolated from Dendrolimus sp..These 4 strains were used as the origin strains B0.Strains H1,H2,H3 and H4 were obtained by repeat passage through the larvae of M.alternatus, while strains R1,R2,R3 and R4 were obtained by repeat passage through the PPDA media.Toxicity of origin and passage strains was measured.Results showed that after being cultured on PPDA meida,the virulence decreased step by step between sucessive generations,irrespective of the high-virulent strains（B5 and Bxs） or the low-virulent strains（B11 and BZ）. For each of the strains,significant differences in LT50 were observed between the mother generation and the filial different generations.Virulence of strains isolated from M.alternatus larvae had different change way from those not isolated from M.alternatus larvae,though all of them were cultured with the same batch of M.alternatus larvae.For example,the virulences of B5,Bxs and B11 strains isolated from M.alternatus larvae tended to increase after being reared for several generations,and the LT50 differed significantly between each of the generation.However,the virulence of BZ isolated from Dendrolimus larvae had no obvious difference between different generations.The difference in virulence changes in the B.bassiana strains may be related to specialization with their host insects.