| The 3rd 14th main-stem leaves of transgenic cotton, Bollgard Ximian33B, have significant effect on the laboratory susceptible cotton bollworra SUS2 (Helicoverpa armigera (Hubner)). After neonates feeding on the leaves for 5 days, the mortality was 90.0-100.0%, and no surviving larvae developed to 3rd instar. This results showed good efficacy of the leaves against neonates of the insect and high Bt expression. While the mortality of CK was 0.0-44.3%, and the survival larvae were mainly in 2nd and 3rd instars, which was 1-2 stadium more than larvae feeding on transgenic cotton. So, the leaves from transgenic cotton suppressed significantly larvae growth of cotton bollwom.Primary assessment of efficacy of transgenic cotton leaves from three lines (Sumian 102> Sumian 191 and Sumian 310) on SUS2 neonates was conducted. After the neonates feeding on the 3rd, 5th, 10th and 15th main stem leaves from Sumianl02, Sumian 191 and Sumian310 for 5 days , the average mortality was 82.0% , 91.0% ^ 75.0% and 52.0%(Sumianl02);62.0%, 86.0%, 65.0% and 36.0%(Sumianl91); 61.0%, 61.0%, 54.0% and 36.0%(Sumian310) respectively. The effect of the three transgenic cotton on SUS2 neonates was significantly or slightly higher than non-transgenic cotton Sumian 12, but lower than Xinmian33B. So efficacy of all three lines should be further improved.The index of detecting resistance to the transgenic Bt cotton was suggested by comparing mortality and growth suppression of larvae of cotton bollworm, which were collected from transgenic Bt cotton field of Xinji city, Hebei Province and non-transgenic cotton field of Fengxian, Jiangsu Province and susceptible strain(SUS2), feeding on leaves for 5 days from Xinmain33B and Sumian 12 respectively. We consider that those few larvae which reached to middle of 2rd instar with above 0.8mg body weight/larva after neonates feeding on transgeniccotton leaves for 5 days were resistant. A F2 genetic detection method of isofemale lines (F2 screen) was established to detect frequency of resistance alleles to transgenic cotton in field cotton bollworm population. 128 isofemale lines were collected from one year growing transgenic cotton area in Qiuxian county, Hebei Province, and the freguency of resistance alleles were detected by the method. The result showed that the frequency of resistance alleles of the cotton bollworm population to transgenic Bt cotton was more than 5.8X i()'3. This detection method will be extend the sensitivity of allele frequency estimation for recessive traits by more than an order of magnitude compared with dose response mortality(resistant ratio) and discriminating dose assays. This method will be suitable to estimate resistance allele frequencies in the wild population and early detection of resistance. Since the frequency of resistance allele has reached or slightly exceeded the assumption (p<103) in refuge plus high dose strategy, preventive cotton bollworm resistance management strategy and measures should be worked out and implemented as soon as possible.The No. 120 isofemale line from cotton field in Qiuxian County, Hebei Province was selected on transgenic cotton Xinmian33B leaves for 6 generations in laboratory. The results showed the susceptibility of this selection populction to Xinmian33B decreased compared with before selection. After 5 days feeding on transgenic cotton leaves, a few survival larvae have developed to middle of 2nd instar with above 0.8?.2mg body weight/larva (reachel to resistant index) in the selection population, but not in CK strain. The results showed H. armigera could have resistant risk to transgenic cotton. During selection, the larval stage of selected population reached to 18.5?.0~23.4?.2 days from 16.0?.5 days before selection., therefore the refuge plus high dose strategy should be studied further.The susceptibilities to biological pesticide Bt (Dipel) in Laboratory selected population from No. 120 isofemal line in each generation during selection were determined. The results showed the LCW value (0.25~0.55mg/ml) and LC95... |
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