Abstract: Biological control of Phyllotreta striolata was explored by isolating and screening highly virulent Bt strains.A strain was isolated from the soil of Hainan Province,which was identified using morphological and molecular methods as a Bacillus thuringiensis strain and named as BS128,and the strain contained a novel insecticidal coding gene Cry8Ga.Laboratory assay of the strain showed a 3-d LC₅₀ of 60.0093 μg/mL against P.striolata.Field tests showed a control efficiency of 67.66% against P.striolata at 15 d post-treatment using 250 μg/mL BS128 suspension 9000 mL/hm² as soil treatment and control efficacies of 61.86% and 62.16% against P.striolata at 7 d and 10 d post-treatment using 250 μg/mL BS128 suspension 9000 mL/hm² as foliar spray,respectively.The results indicate that soil treatment using the strain achieved equal control of P.striolata to that of foliar spray.We believe that soil treatment using the strain is more suitable for control of P.striolata,because the soil treatment using the strain against P.striolata larvae in the soil can lessen the damage of adult beetles in the seedling stage and,Bt is more effective in the soil and has a longer persistence,which avoids the inactivation of foliar sprayed Bt by high temperature or strong UV radiation.

Key words: Phyllotreta striolata, Bacillus thuringiensis, bioassay, field control efficiency