Synergism of CmGV and Bacillus thuringiensis against larvae of Cnaphalocrocis medinalis Güenée

The toxic potency of Cnaphalocrocis medinalis granulovirus(CmGV)and the synergism of CmGV combined with Bacillus thuringiensis(Bt)against C.medinalis were studied by bioassay in laboratory.The strain of CmGV-05had the highest toxicity to the larvae of C.medinalis.The LC50 value was 178.78mg·L-1.Different ratios of CmGV combining with Bt indicated the existing of the prominent synergistic effects,with the co-toxicity coefficient(CTC)from 124.92to 160.47against larvae of C.medinalis.Field tests showed that the compound(1×105 OB·mg-1 CmGV+ 16 000U·mg-1 Bt)had obvious control effect on the larvae.The effects of larva killing and leaf protection of different doses were 62.68% to 75.16% and 65.27% to71.19% in the first 3days,and 82.63% to 89.3% and 78.53% to 85.12% after 7days of treatments.After 14days,the effects of larva killing and leaf protection were still 80.41%to 87.01%and 78.26%to 83.49%.It was indicated that the combining CmGV with Bt had synergistic effect.Compared with CmGV alone,the initial infection time of death shortened about 3days,mortality increased 20.23%,and sustainable effect was up to 30days.