The Initial Frequency Of Resistance Alleles To Cry1Ab In The Hexian Population And Baseline Susceptibility To Cry1A In Field Populations Of Chilo Suppressalis

The rice stem borer, Chilo suppressalis (Walker) is one of the most serious and frequent pests of rice.Currently, chemical control has been a major method for protecting rice from damage by the rice stem borer. However, long-term unreasonable application of pesticides will result in serious insecticide resistance in C. suppressalis, and negative impacts on ecological environment. Bt transgenic rice provides an effective, economical and eco-friendly method to control the rice stem borer. At present, two Bt transgenic rice lines expressing a fused gene derived from crylAb/crylAc have passed through biosafety risk assessment in China, and this indicates that Bt transgenic rice will be commercialized in China.Before Bt rice is released for commercial planting, detecting the frequency of resistance alleles to Bacillus thuringiensis in field populations of C. suppressalis and establishing baseline susceptibility to Bt toxins of different geographical populations, will provide an important basis for the implementation of resistance monitoring of C. suppressalis and the formulation of resistance management measures in future. In this study, we used an F2screen method to estimate the frequency of resistance alleles to CrylAb in a field population of C. suppressalis collected from Hexian, Anhui Province in2011. We also measured the toxicity of Bt toxins CrylAb and Cry1Ac in10field populations collected from the middle and lower reaches of the Yangtze River in2012. Our results will lay an important foundation for Bt resistance monitoring and management.1-Using the F2screen method to estimate the frequency of resistance alleles to CrylAb in a field population of C. suppressalisEgg masses of the first generation of C. suppressalis were collected from Hexian, Anhui Province in May of2011. Each egg mass was used to build a single isofemale line and a total of112isofemale lines were screened at F2generation. The frequency of resistance alleles to CrylAb was estimated to be0.0088(95%CL:0.0083-0.0258). The results showed that the frequency of resistance alleles to Cry1Ab in Hexian population of C. suppressalis was higher than expected, and it would be possible to evolve resistance to CrylAb in field population. So we should adopt some resistance management tactics in advance.2. Baseline susceptibility to CrylAb and Cryl Ac in field populations of C. suppressalisSusceptibility to Cry1Ab and Cry1Ac in10field populations of C. suppressalis collected from the middle and lower reaches of the Yangtze River in2012was investigated. The results demonstrated that the LC50of Cry1Ab ranged from0.071to1.246ug/100ul and17.5-fold variations occurred among populations, and the LC50of Cryl Ac ranged from0.057to1.094μg/100μl and19.2-fold variations occurred among populations. The significant differences in Cry1Ab and Cry1Ac susceptibility among field populations suggested that there were high risks of evolution of resistance to CrylAb and Cry1Ac in field populations of C. suppressalis. Furthermore, the correlation analysis showed that there was a moderate positive correlation (r=0.689,p=0.0275) between the LC50values obtained for Cry1Ab and Cry1Ac across the ten populations of C. suppressalis, suggesting that the C. suppressalis populations which are relatively tolerant to one toxin are also relatively tolerant to the other.