Resistance Monitoring of Helicoverpa armigera (Hübner) to Bacillus thuringiensis Insecticidal Proteins in North China

Bioassay methods of Bt resistance in cotton bollworm,Helicoverpa armigera (Hubner) were studied. The results showed that the best time for investigating the mortality were 5 days after Bt treatment and 14 days after MVP treatment. Four field populations from three provinces of north China were collected in 1996~1998 for monitoring of resisance to Bacillus thuringiensis (Bt). The resistance ratios (RRs) to Bt formulation produced by Bt kurstaki were 1.3~5.3 folds in three years compared with a susceptible population from Xinjiang. Resistant individuals at 0.9% were found in 1998 in one population by using diagnostic dose. In 1998, the resistance grade of Bt cotton declined against Qiuxian,Jizhou and Gaomi populaions compared with a laboratory population. The relative RRs were 4.6,3.9,3.8 folds to CryⅠAc and 1.1,1.4,1.6 folds to Bt formulation, respectively. CryⅠAc was more suitable than Bt formulation to be used for resistance detection to Bt cotton.