Studies On Frequency Of Resistance Allele To Transgenic Bt Cotton In Field Helicoverpa Armigera (H(?)ber) And Its Monitoring Method

Cotton bollworm (Helicoverpa armigera (Hubner)) was an important worldwide pest that damaged cotton. In China, cotton bollworm had already developed resistance to several kinds of insectisides because of the slather using of chemical pestiside. Since 1998, genetically engineered cotton ( Bt cotton ) that produced an insecticidal protein originally found in the biocontrol agent, Bacillus thuringiensis (Bt), has been planted millions hectares every year in China. Because these toxins were produced by the plants from seedling stage to harvest, there would be intense selection for the resistant genotypes of the pest as the acreage planted to this transgenic cotton increase. Therefore, widespread adoption of Bt cotton increase the risk that pest would evolve resistance than that of the Bt biocontrol agents. Doctor Fengxia Meng had studied that the inheritance trait of resistance in laboratory selected cotton bollworm strain was incompletely recessive, so there were no proper general methods to monitor the early resistance in cotton bollworm population to Bt cotton . From 2000 to 2002, we used F₂ method of isofemale lines (F2 screen) to monitor the change of resistance alleles frequency in the field population of cotton bollworm to transgenic Bt cotton, NuCOTN 33" in Heibei Province where Bt cotton had planted since 1998 . Furthermore, we established an F1 method of isofemale lines to detect quickly and conveniently the frequency of resistance alleles to transgenic cotton in field cotton bollworm population. The goals of our research were to offer scientific evidences for resistance management and to prolong the application of Bt cotton.In 1999, He et al used the F2 method to detect the frequency of resistance alleles to Bt toxin from transgenic Bt cotton, NuCOTN 33" , in cotton bollworm. The results showed that the resistance alleles frequency in the natural population of cotton bollworm reached to >0. 58%, in Qiu County,Hebei Province .where transgenic Bt cotton had been planted for only one year. In 2000, we monitored the resistance allele frequency to transgenic Bt cotton, NuCOTN 33" in the field population of cotton bollworm with F2 method, in Wei Xian county and Chengan county, Hebei Province, where transgenic Bt cotton had been planted for three years. And the frequency of resistance allele of the bollworm population had increase to 3.3%. We continued to monitor the frequency of resistance alleles in cotton bollworm to Bt cotton, NuCOTN 33" by F2method, in Wei County, Hebei Province. In 2001, the frequency increased to 6. 9% (in larvae of the third generation); in 2002,the frequency was 6. 9 % (in larvae of the second generation), 7.8% (in eggs of the third generation) and 9.4% (in larvae of the third generation) in field. We could conclude that the frequency of resistance was rising quickly with the time of cotton planted increasingoThe F1 method of isofemale lines was established to detect the frequency of resistance alleles to transgenic cotton in field cotton bollworm population. Virgin females or males that developed from larvae and eggs collected in the cotton field were individually mated to virgin males or females from laboratory resistance strain, respectively. The genotypes of the offspring of all the F1 progeny of each isofemale lines were determined in a Bt cotton assay, the expected frequency and confidence intervals of resistance alleles were calculated using Bayesian statistics described by Andow and Alstad (2000). The results of the monitoring showed that the frequency of resistance alleles to transgenic Bt cotton in the field populations were 8. 8% (in larvae of field second generation), 8. 9 % (in eggs of field third generation) and 9.3% (in larvae of field third generation) in Wei County in 2002, which had no distinguish difference with the research result of the F. method by statistical analysis. The data suggested that the F, method had the same sensibility as that of the F2 method when they were applied to detect (monitor) the rare resistance allele, and the F1 method was mo...