The Analysis Of Bt Cotton Resistance Gene Frequency For Field Populations Of Helicoverpa Armigera

Helicoverpa armigera Hubner (Lepidoptera:Noctuidae), is a serious pest of cotton in China. Transgenic cotton that expresses a gene derived from the bacterium Bacillus thuringiensis (Bt) has been commercially available in China since 1997, holds great promise in contolling H. armigera. Monitoring of field H. armigera population resisitance to Bt-CrylAc toxin, is the base of sustainable utilization for Bt cotton. During In this study, monitored H. armigera populations from Anci County of Hebei Procince and Xiajin County of Shandong Province in Yellow River cotton planting region of China to Bt cotton resistance by the diagnostic concentration method and DNA molecule screen method in 2009-2010. Besides, correlation of tolerance between CrylAc and Vip3Aa in the field H. armigera populations were researched The main research results are as follows:1. In total,1143 isofemale families of H. armigera from Xiajin county of Shandong Province and 1122 families from Anci county of Hebei Province were screened with a discriminating concentration of CrylAc containing diets in 2009-2010. it was estimated that the resistance gene frequency of Xiajin populations in 2009-2010 were 0.00046 and 0. Major resistance alleles to CrylAc in Anci populations were not detected during the two years. The results showed that the frequency of resistance alleles of H. armigera populations in field to CrylAc was remained low(＜0.0001).2. According to one mutant allele of a APN gene linked with resistance to CrylAc in H. armigera. by lab screening, DNA molecule detection technology was used to screen the field of H. armigera resistance gene. In 2009-2010, a total of 1799 larvae derived from CrylAc cotton fields in Anci and Xiajin County were screened, no resistance alleles associated with APN mutation were detected.3. The susceptibility to CrylAc was measured in field-collected H. armigera larvae on different hosts, which included 1-3 generations of H. armigera each year. The F1 offspring of single-pair crosses from a region with high density of Bt cotton planting in the Xiajin's region of the Shandong Province of northern China. During 2008-2010, a total of 258,56,184 and 160 single-pair crosses derived from wheat (first-generation), Bt cotton (second-generation), Bt cotton (third-generation), and corn (third-generation) were successfully screened on Cry1Ac diets, respectively. Based on relative average development rates (RADR) of H. armigera larvae in F1 tests, there were significant differences in the mean RADR from different hosts. The second, third-generation moths emerging from Bt cotton fields show more resistance to Bt toxin compared with first, third-generation moths emerging from wheat and corn each year. Furthermore, RADR increased from 2008 to 2009 in all three crops, but no further increase occurred from 2009 to 2010 in any of the three crops examined. These results may indicate that indeed, susceptibility to Bt toxin decreased in current field populations of H. armigera from 2008 to 2009 and 2010, and the present study also indicate that corn play an important role in maintenance of H. armigera susceptibility to Cry1Ac toxin although the value for corn functioning as refuge host crop is limited as this crop is planted in small areas in the Xiajin Bt cotton growing region.4. In total,80 isofemale families of H. armigera from Xiajin County of Shandong Province and 93 families from Anci County of Hebei Province were screened with a discriminating concentration of both CrylAc-and Vip3A-containing diets in 2009, and percentage of larval weight inhibition of F1 full-sibfamilies tested simultaneously on CrylAc and Vip3Aa. Results indicate that responses to CrylAc and Vip3Aa were not genetically correlated in current field population of H. armigera.The current studies indicate that the frequency for Bt resistance allele are still rare in the current field population of H. armigera, although Bt-Cry1Ac cotton in north China has planted more than 10 years, it show that non-cotton hosts potentially provide natural refuge for H. armigera, thereby slowing the evolution of resistance to transgenic cotton expressing the B. thuringiensis CrylAc toxin. In consideration of responses to CrylAc and Vip3Aa was not cross-tolerance in field population of H. armigera, transgenic cotton expressing Vip3A can be used for the Cry1Ac toxin resistance management of H. armigera in China.