| By field systematic investigation, the characters of Arthropod community structure and dynamics, temporal pattern, numeric dynamics of dominant pests and natural enemies in cotton-pasture intercrop field in Dunhuang from May to October in 2004 were investigated using the knowledge and theory of community Ecology in order to enrich the theoretical foundation for IPM of pests. The research contents and results were listed as follows: 1 Composition of arthropod community in cotton-pasture intercrop field In cotton-alfalfa (Medicago sativa) intercrop field, total 78 species of arthropods were observed, which belong to 72 species, 42 Families, 10 Orders of Insecta and 6 species ,2 Orders of Arachnida. The ratio of natural enemies and pests of arthropod communities was 1∶13.6177(0.0734). Total 76 species of arthropods were observed in cotton-prairie milk vetch (Astragalus adsurgens) intercrop field, which belong to 70 species, 36 Families,10 Orders of Insecta and 6 species, 2 Orders of Arachnida,. The ratio of natural enemies and pests of arthropod communities was 1∶16.435(0.0608). In cotton-Vicia villosa intercrop field, total 75 species of arthropods were observed, which belong to 69 species, 36 Families,10 Orders of Insecta and 6 species, 2 Orders of Arachnida. The ratio of natural enemies and pests of arthropod communities was1∶15.9898(0.0625). In cotton-spring vetch (Vicia sativa) intercrop field, total 74 species of arthropods were observed, which belong to 68 species, 35 Families,10 Orders of Insecta and 6 species, 2 Orders of Arachnida,. The ratio of natural enemies and pests of arthropod communities was 1∶18.8225(0.0531). In cotton field, total 71 species of arthropods were observed, which belong to 65 species, 32 Families,10 Orders of Insecta, and 6 species, 2 Orders of Arachnida. The ratio of natural enemies and pests of arthropod communities was 1∶38.5861(0.0259). Species of every fields were compared and the results were listed as follows: cotton-alfalfa intercrop field>cotton-prairie milk vetch intercrop field>cotton-Vicia villosa Roth intercrop field>cotton-spring vetch intercrop field>cotton field. Although the results were so, species difference among arthropod community in different cotton field was not obvious. The ratio of natural enemies and pests of arthropod communities in every fields were compared and the results were listed as follows: cotton-alfalfa intercrop field>cotton-Vicia villosa Roth intercrop field>cotton-prairie milk vetch intercrop field>cotton-spring vetch intercrop field>cotton field. Based on the knowledge and theory of community Ecology, intercropping pasture in cotton field could provide more shelter and necessary food for natural enemies. So ratio of natural enemies and pests increased. Therefore, dominance and dominant concentration of cotton-pasture intercrop field was lower than that of cotton field, but evenness, species richness and diversity was the largest and control efficiency of natural enemies to pests was better than others. It is suggested that intercropping alfalfa in cotton field was the optimum methods 2 Temporal dynamics of Arthropod community in cotton-pasture intercrop field The methods of diversity exponent, evenness exponent, richness, principal component analysis and optimal sorting method were used to study the community structure and temporal pattern of arthropods in cotton-pasture intercrop field in Dunhuang. The results showed that the difference and regularity of species richness, the diversity and evenness of the arthropod community at different time were obvious. The main factors and temporal patterns of arthropod community in the course of seasons were obvious. Based on the results, the temporal patterns of arthropod community in cotton-pasture intercrop field could be divided into several different stages. Considering the climatic and phonological development, the characteristics of the pests and the natural enemies occurring in each stage were analyzed. According to the systematic and studies, the main factors influencing arthropod community was studied by using principal component analysis. The results indicated that the main influential factors have Aphis gossypii, Empoasca biguttula, Tetranychus dunhuangensis, Miridae, Thrips spp., Adonia variegate, Araneae, Synharmonia conglobata contaminata, Orius similes. The temporal patterns of arthropod community could be divided by using optimal sorting method. The temporal patterns of arthropod community in cotton-alfalfa intercrop field and cotton-prairie milk vetch intercrop field could be divided into five stages and the others could be divided into four stages. Numeric dynamics of arthropods were closely related with cotton growth periods. The results showed that the characteristics of arthropod community in cotton-pasture intercrop field and cotton field was obvious in the course of season. Especially to phonological development, with the cotton growth periods processing, arthropod community succession occurred constantly. From the shoot period of cotton to the flower and ball period of cotton, the species and number of arthropods became more and more rich; the number of pests and their natural enemies decreased gradually during the ball opening period of cotton. 3 Interaction of ecological exponents of cotton-pasture intercrop field Multiple regression analysis was adopted to study the relationship among species richness, evenness and diversity. It is found that they have certain positive correlation. Evenness has stronger effect on diversity than species richness. Arthropod community Characteristics of different cotton cropping systems was studied by using R-factor clustering. Arthropod communities in 4 cotton-pasture intercrop field belong to the same cluster and arthropod community in cotton field belong to 1 cluster alone. It is suggested that intercropping pasture in cotton field made community diversity increase and kept community structure and component reasonable.
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