| The structures of arthropod communities and population dynamics of the main pests and natural enemies in the transgenic Bt cotton, transgenic CryIAc and CpTI cotton, and traditional cotton fields were investigated. In the study of arthropod communities, the guilds and nutrition classes were applied, and the migration of natural enemies round the cotton fields was analyzed. The ecological effects of transgenic Bt cottons on Propylaea japonica were studied by raising Propylaea japonica with Aphis gossypii feeding on Bt cotton in laboratory. The main results are showed as follows:1．88 species of arthropods belonging to 12 orders, 53 families, were found in cotton fields, which included 39 phytophagous pests, 40 enemies and 9 neutral arthropod species. They were divided into 29 guilds, 8 groups and 3 nutrition classes including basal, intermediate and top species.By the comparison of diversity indexes of the species, guilds, groups and nutrition classes, the same dynamics was showed: diversity indexes of species>diversity index of guilds> diversity indexes of groups> diversity indexes of nutrition classes. Because of the similarity of diversity indexes of species and diversity index of guilds, the analysis of arthropod communities in term of guilds rather than species made it easier to analyze the complicated relation of pests and enemies, which is one of the methods to study the species function of arthropod communities.2.Comparing the species number of transgenic Bt cotton---GK12 fields with conventional cotton---Simian3 fields, the natural enemy increased by 12.38%, neutral arthropod 25.33%, and the pest number was about the same, with higher mean number of diversity index. Comparing the transgenic CryIAc and CpTI cotton with the conventional cotton, the enemy and the pest number decreased by 4.56% and 55.74% respectively, the neutral arthropod number increased by 16.17%, with the total arthropod number declining obviously, and the mean number of diversity index was higher. Moreover the decrease of the dominance index in the SGK321 field benefited to the stabilityof arthropod communities and the ecological balance in cotton fields. In the analysis of arthropod communities in the cotton fields, Simian3, GK12 and SGK321 were put into one group, and Shiyuan321 and 33B another group, because of their similar community structure. 4 stages of development were divided in term of time. The principal component analysis of arthropods in cotton fields suggested that 4 components of spiders, pests, neutral arthropods and predator enemies, and parasitic enemies could be used to analyze the arthropod communities in transgenic Bt cotton and conventional cotton fields.3.Transgenic Bt cotton and transgenic CryIAc and CpTI cotton had the good control effect on the cotton bollworms, with very small numbers of the first and second generation population and smaller number of the third generation population than in the conventional cotton fields. Comparing with GK12 and 33B, the damage index of leaves in the second generation of cotton bollworms on SGK321 and falling number of squares decreased by 295~430% and 350~800%, and the resistance declined after that. The transformation of CpTI into Shiyuan321 cottons improved the resistance to cotton bollworms, and prolonged the life span of transgenic cottons.Due to the decrease of chemicals usage, the damage of green leaf bug to GK12 tended to be heavier while the damage to SGK321 was controlled to some degree. 4. Among the predatory enemies, the number of Orius minutus, Campylomma diversicornis Reuter on GK12 and 33B cottons decreased by 21.70~37.63% compared with the number on Simian3 cottons, and the number on SGK321 decreased by 4.55~42.98% comparing with the number on Shiyuan321. However, the number of ladybirds and green lacewing on GK12 and 33B increased by 8.23~17.06% compaed with the number on Simian3 cottons, and the number on SGK321 increased by 24.05~25.40% compared with the number on Shiyuan321. In different cotton fields, the control of enemy guilds...
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