| Based on the methods of ecological community and system investigation, the effect of transgenic Bt cotton on the historical level, the whole structure of arthropod community and the seasonal fluctuation of target pests and non-target insects were evaluated in cotton field in Julu, HeBei during 2001-2002. There were four treatments in the trials: transgetic Bt cotton-Borgard (B), or JiKang 668(JK668) and common cotton - control(C), non-control(CN).The main results were as follows: 1 The effect of transgenic Bt cotton on the whole arthropod communityCompared with C, the species richness in B, CC30 (or JK668) appeared certain change (in 2001, B reduced by 2.33%, JK668 reduced by 9.30%; in 2002, B increased by 4.44%, JK668 reduced by 4.44%), the number of total individual increased by 60.64% in 2001, 158.87% in 2002. The constitution and order of the dominant species in phytophagous subcommunity changed and the number of total individual in transgenic Bt cotton field increased by 57.02% in 2001, 173.59% in 2002 (compared with the C). The number of total individual of the predatory subcommunity and parasitic subcommunity increased by 30.64% in 2002 but reduced by 20.81% in 2001.The order of diversity and evenness value of four treatments were: in 2001, JK668 (2.0314,0.5545), B (1.7624,0.4715), C (1.7314,0.4610), CN (1.2741,0.3388); in 2002, C (1.6481,0.4329), B (1.1546,0.2999), JK668 (0.9616,0.2557), CN (0.8311,0.2196). The dominant value were: in 2001, CN (0.3629), C (0.2635), B (0.2606), JK668 (0.1834); in 2002, JK668 (0.5139), CN (0.5054), B (0.4255), C (0.2995). These results shows: the diversity and evenness of two kinds of transgenic Bt cotton were higher than CN, indicating the structures of arthropod community in transgenic Bt cotton fields were more superior and reasonal than those in CN cotton field; the evenness of the species of arthropod community appeared certain fluctuation and the dominant values were higher, indicating the possibility of disaster occurrence of certain pest. 2. The effect of transgenic Bt cotton on target pests(1) The effect on the number of Helicoverpa armigera (Hubner) eggs per 100 plantsThere were no obvious difference in all treatments according to the two-year investigation. In the period of the second generation H. armigera eggs(6.18-6.30), the number of eggs in two kinds of transgenic Bt cotton fields(B and JK668) were more than non-transgenic Bt cotton fields, indicating the transgenic Bt cotton hadn't repellency to the H. armigera oviposition, even traped the adults of H, armigera to lay eggs sometimes.(2) The effect on the number of H. armigera larvaes per 100 plantsIn the whole growth period, the number of young larvaes in B and JK668 cotton fieldsare less than common cotton, the number of older larvaes were also less than common cotton in the initial period but were high or higher than non-resisitance cotton in the occurring peak of the third and fourth generation of H. armigera, indicating the resistance owned more obvious characters of seasonal dynamics. In a word, B had the best resistance for the H. armigera of the second generation and had better resistance for the third generation, but had worse resistance for the fourth generation. 3 .The effect of transgenx Bt cotton on non-target insectsThe kinds of the dominant species of pests in transgenic cotton field had obvious change, in which the H. armigera was no longer the main pest and the piercing-sucking pests such as Aphis gossypii, Tetranychus urticae, Thrips tabaci etc. rose the main pests. The kinds of the dominant species of predatory natural enemies seemed to be no variation, which was still Propylaea japonica Thunberg. Because of the effect of transgenic Bt cotton on H. armigera laevae-the development delay, the weight reduction, which affected the qualities of parasitic enemies, leading to the reduction of the weight of cocoon and the weight of adult, and the reduction of H. armigera laevae number in cotton field, the number of parasitic enemies reduced obviously and the change of dominant species...
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