Studies On Resistance Screening, Monitoring And Resistance Mechanism Of Helicoverpa Armigera (Hübner) To Transgenic Cotton

The transgenic cotton expressing the Cry1Ac toxin shows an excellent effect on controlling the occurrence and damage of cotton bollworm. Meanwhile, the cultivation of Bt cotton also brought potential ecological and environmental security risk, in particular, the risk of resistance to transgenic cotton has been much attention at nation and abroad. The effects of transgenic cotton on cotton bollworm fitness, enzyme activities and genetic differentiation, at the same time, detection for the frequency of resistance to Cry1Ac in field were studied by lab feeding, chemistry analyzing, field monitoring from the view of biology, biochemistry, molecular biology. This paper based on cotton bollworm resistant strains (AYBC, AYBT) and the control strain (AYCK) which selected 17 generations by artificial feed mixed cotton seed powder, used the same method continued screening to 26th generation. And use it as test insects, the effects of transgenic cotton on cotton bollworm fitness, enzyme activities and genetic differentiation, as well as, monitoring for the frequency of resistance to Cry1Ac in the Yellow River Basin during 2007~2009 were studied by lab feeding, chemistry analyzing, field monitoring from the view of biology, biochemistry, molecular biology. The main results and conclusions as following:1. After 26 generations of selection, compared with the susceptible strain, in the AYBC and AYBT strain, larval development period was delayed; pupal weight, fecundity and egg hatching rate were reduced. Compared with AYBT strain, larval development period was delayed; fecundity was reduced. After 26 generations of selection, resistance to Cry1Ac of the AYBC strain and AYBT strain increased to 5.63 fold and 11.44 fold, respectively, compared with that of the susceptive strain. The analysis of changes in resistance of these two strains revealed that the screening material in AYBC strain could effectively delay the evolution of resistance to Cry1Ac in bollworm.2. We determined enzymes activities in larvae of H.armigera which from AYBC strain and AYBT strain. The results have demonstrated that: compared with the control, in AYBC strain, the activities of GSTs, ACP, chymotrypsin-like enzyme and weak alkaline trypsin-like enzyme were reduced; the activities ofα-naphthyl acetate esterase, ALP and three protective enzymes (SOD, CAT, and POD) were increased. In AYBT strain, the activities of AchE, chymotrypsin-like enzyme and weak alkaline trypsin-like enzyme were reduced; the activities of GST, SOD, POD, CAT, APN and active alkaline trypsin were increased. Compared with the AYBT strain, in AYBC strain, the activities of two trypsin-like enzymes were reduced; activity of chymotrypsin-like was not obvious change.3.During 2007~2009, we used genetic method of isofemale lines F1/F2 to detect the frequency of Bt resistance genes in Helicoverpa armigera populations which collected from Anyang County, Weixian County and Wucheng County. The results show that the tolerance levels of Helicoverpa armigera to Cry1Ac was highest and tended to decline during 2008~2009 in Wucheng population, higher and tended to increase year by year in Anyang population, and have not significant change in Weixian population.4. The optimal RAPD system for H.armigera was established. Based on this, the study used RAPD technique to analyze the genetic differentiation of populations from lab screening and field in 2009. The results show that, in population from lab screening, the genetic distance of clustering populations was 0.161 for AYBT strain, 0.177 for AYBC strain, and 0.213 for AYCK strain. Each population was clustered at first, and the genetic distance (0.402) of clustering for one species. The above result indicated that there was a significant genetic differentiation after 26 generations of selection. In field population, the genetic distance of clustering populations was 0.524 for Anyang population, 0.437 for Wucheng population, and 0.446 for Weixian population. Each population was clustered at first, and the genetic distance (0.610) of clustering for one species. The above result indicated that there was a clear geographical differentiation among the populations from three regions.