Pathogenicity of a Beauveria bassiana(Balsamo)Vuillemin isolate to daikon leaf beetle,Phaedon brassicae Baly(Coleoptera: Chrysomelinae)

The daikon leaf beetle,Phaedon brassicae,is an important insect pest of cruciferous vegetables in South China.It is typically controlled by synthetic insecticides.A search was made for alternative control methods,and diseased daikon leaf beetles were collected and screened for potentially useful pathogens.A Beauveria bassiana isolate,SCAU-BB01D,originally derived from P.brassicae adults was found to infect all stages of the beetle under laboratory conditions.The pathogenicity of the isolate was investigated by immersing P.brassicae larvae and adults into serial dilutions of B.bassiana(10~5—10~8 conidia/ml).The highest concentration(10~8 conidia/ml) treatment caused an adult mortality of 84.7% on day 14,and larval mortalities of 94.0%,96.0%,and 81.0% for instars I, Ⅱ,Ⅲ on day 10,respectively.A time-dose-mortality model was used to analyze the bioassay data and the model fitted the data well,resulting in parameters for estimating the time and dose effects.The LC_(50) values of instar Ⅰ—Ⅲ and adult were 1.07×10~6,1.63×10~5,and 8.31×10~6,2.68×10~7 conidia/ml,respectively,on day 10 after treatment.The LC_(50) value on day 14 was 2.38×10~6 conidia/ml for adults.The lethal time for the isolate on P.brassicae varied with the insect stage.At a concentration of 10~8 conidia/ml,the LT_(50) values of the isolate against adult and instar I,instar Ⅱ,and instar Ⅲ larvae were 9.28,4.29,4.40 and 5.06 d,respectively.The results indicated the potential of the isolate for use in microbial control of P.brassicae.