| Bt transgenic cotton has been a worldwide important tool to control pests of cotton field since 1990s. Today, north China and Yantz River valley have deployed Bt cotton gradually. In order to undertand resistance level of Bt cotton to targeted insects in Yantz River valley and make the best use of its control effecicency to pests in this region, seasonal expression profile of insecticidal protein of two Bt cotton lines carrying a CrylA gene from Bacillus thuringiensis subsp. kurstaki (Berliner), developed, respectively, by Monsanto Co. and Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, and their influence on targeted pests and non-targeted pests were investigeted.Results showed that the toxin content in Bt cotton changed significantly over time, and that the structure, growth stage, and cultivar were significant sources of variability (P < 0.05), but there was no significant difference between the two years (P = 0.8362). Generally, insecticidal protein levels were high during the early stages of cotton growth; they declined in mid-season, and rebounded in late season. On most dates sampled, the toxin contents in leaf, square, petal and stamens (including non-ovule pistil tissue) were much higher than those in ovule and boll. Compared to BG1560, the expression of CrylAc/CrylAb protein in GK19 was more variable during the whole growth period of cotton.Bioassay fed on structures of two Bt transgenic cotton lines to cotton bollworm (Helicoverpa armigera) indicated that there were significant differences of resistance levels among various structures and developmental stages of both Bt transgenic cotton lines. In general, resistance level of reproduction organs were higher than leaves in two lines, and it decreased gradually as cotton growth from July to September; The field evaluation on larval population dynamics of H. armigera in Bt and conventional cotton showed that the larval densities in GK19 and BG1560 fields decreased, respectively, 92.04% and 81.85% in 2001, and 96.84% and 91.80% in 2002. However, egg densities of cotton bollworm in two Bt cotton fields were no significant difference from conventional lines, and distrubiton of cotton bollworm larvae on structures of two Bt cotton was similar to that on structures of conventional cotton.Survey on egg density and larval population dynamics of pink bollworm in Bt and non-Bt cotton fields showed that there were no significant differences in egg density among the two Bt cotton lines and conventional cotton lines, but larval densities on both Bt lines were significantly lower than on the conventional lines in both years. In comparison with the larval density on a conventional line without chemical control, the control efficacy in different growth stages of two Bt cotton lines were 73 - 100% for GK19 and 89 - 100% for BG1560, they were higer than control efficiency of 54 - 88% for chemically treated conventional cotton.Bioassay fed on structures of Bt cotton lines and Bt formulation, effects of Bt cotton on survival of common cutworm were studied. Results showed that mortalities of common cutworm fed on leaf, petal, and flower heart among lines were no difference, but compared with correponding treatments, mortality of common cutworm fed square of BG1560 was higher. LC50 of common cutworm to Bt insecticide was 1170PPm. Investigation in field displayed that larval densities in two Bt cotton lines were nosignificant difference from conventional cotton line. The life table analysis in the laboratory showed that there were no significant differences in survival rate, nympha duration, and fecundity between laboratory populations of aphids fed on Bt and non-Bt cotton. The field surveys also indicated that there were no significant differences in population dynamics of aphids and its damages to different cotton lines between Bt cotton and conventional cotton fields.By systematic evaluation on resistance of Bt cotton planted in Mid-Yangtze River valley to major targeted pests and potential impact on population dynamics of non-targeted...
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