| Cotton is the most important cashing crop, and often attacked by many pests, in southern Xinjiang. Arthropod community structure and functions in cotton and some influencing factors of arthropod community and major pest population were studied with the principles and methods of community ecology and population ecology to meet the need of cotton SPM (Sustainable Pest Management) at Shache county in this region in 2002-2006. The results were as follows:1. Arthropod community structure in cotton-wheat-alfalfa ecosystemBy sampling with an electric sucker refitted with WFB-20AC Sprayer (Beijing Fengmao Plant Protection Machine Company) by Institute of Plant Protection, Chinese Academy of Agricultural Sciences, and sweep net, a total of 403 arthropod species were collected from cotton field, of which 382 belong to Insecta, 20 belong to Arachnoidea, 1 belong to Chilopoda. The orders with high species richness were Hymenoptera (168 species), Diptera (90 species), Coleoptera (44 species), Homoptera (26 species), Hemiptera (23 species), Araneida (18 species) and Lepidoptera (12 species). The families with highest species richness were Ichneumonidae (22 species) and Eulophidae (21 species). Of all arthropod species, 141 were herbivorous arthropods, 229 were carnivorous arthropods, 33 were omnivorous and saprophagous arthropods; 33 were cotton pests, 226 were natural enemies (91 predator species and 135 parasitoid species), 144 were neutral arthropods.In cotton field, orders with high relative individual abundance were Homoptera (54.67%), Thysanoptera (29.39%), Diptera (6.01%), Hemiptera (4.54%), Coleoptera (2.52%) and Hymenoptera (1.30%); families with high relative individual abundance were Aphididae (53.04%), Thripidae (28.43%), Miridae (3.64%), and Coccinellidae (2.33%). Relative individual abundances of herbivorous arthropod, carnivorous arthropod, total of omnivorous and saprophagous arthropod were 88.73%, 9.07%, and 2.20%; and those of cotton pest, natural enemy, and neutral arthropod were 84.33%, 9.07%, and 6.60%, respectively.In cotton field, the dominant cotton pest species were Aphis gossypii Glover and Thrips tabaci L., abundant cotton pest species was Acyrthosiphon gossypii Mordvilko, frequent cotton pest species were Lygus pratensis L. and Empoasa bipunctata ulmicola A.Z.; the dominant natural enemy species were Hippodamia (Adonia) variegata (Goeze), Campylomma diversicornis Reuter, and Deraeocoris punctulatus Fall, abundant natural enemy species were Aeolothrips fasciatus (L.) and Orius niger Woiff, and 10 other species were frequent natural enemy species; the abundant neutral arthropod species were sp1 of Ceratopogonidae, sp1 of Drosophilidae, and Delia platura (Meigen), and the number of abundant and frequent neutral arthropod species were 4 and 8 respectively.248, 196, and 257 arthropod species were collected from wild vegetation at the margin of cotton field, from wheat field, and from alfalfa field. The relation of arthropod community in cotton field and in these three non-cotton habitats was also studied. The sub-community of herbivorous arthropods in cotton field was more similar with those in alfalfa field and in wild vegetation at the margin of cotton field, than that in wheat field. The sub-communities of carnivorous and saprophagous arthropods in cotton field were more similar with those in alfalfa field and in wheat field, than that in wild vegetation at the margin of cotton field. The sub-communities of omnivorous arthropods in cotton field were more similar with those in wheat field and in wild vegetation at the margin of cotton field, than that in alfalfa field.2. Effects of wheat-cotton overall arrangement mode on the structure and diversity of arthropod communities in cotton fieldsThe influencing effects of wheat-cotton overall arrangement mode on the structure and diversity of arthropod communities in cotton fields were studied by sampling with the mean of nude-eye inspection. The more evenly were wheat and cotton fields distributed, the less total cotton pest arthropod individuals and the more total natural enemy individuals were found in cotton fields. Compared with the cotton fields arranged alternatively with or adjacent to wheat fields, continuous large area mono-planted cotton fields had more total cotton pest arthropod individuals, neutral arthropod individuals, aphids, spider mites, Aeolothrips fasciatus (L.), and ladybirds, less total natural enemy individuals, cotton thrips, spiders, similar number of Lygus pratensis L., Helicoverpa armigera Hubner, predacious hemipteran bugs, and Paederus fuscipes Curtis. Diversity index of cotton pest arthropods was not influenced by wheat-cotton overall arrangement mode. Species richness and dominant concentration index of cotton pest arthropods, and species richness and diversity index of natural enemy, showed different results in 2 years experiments, suggested there should be other influencing factors except wheat-cotton overall arrangement mode to be studied.3. Effects of alfalfa and rape lines planted on the ends and margins of cotton fields on arthropods in cotton fieldThe influencing effects of alfalfa and rape lines planted on the ends and margins of cotton fields on arthropods in cotton fields were studied by sampling with the mean of nude-eye inspection. Alfalfa lines increased the number of cotton thrips and natural enemies except lady beetles, but reduced the number of spider mites and neutral arthropods, while rape lines increased the number of lady beetles, aphids, and spider mites, but reduced the number of cotton thrips in cotton. Cotton fields with these two crop lines had more abundant natural enemies which not only controlled different pest arthropods before these two crops were harvested but also laid a solid foundation for the control of cotton pests including cotton bollworm appeared after late-June.4. Efects of Bt cotton on diversity of arthropods in cottonThe effects of Bt cotton and chemical control on diversity of arthropods in cotton were studied by sampling with electric sucker and sweep net. Bt cotton did not influence the diversities of cotton pest arthropod, natural enemy, and neutral arthropod sub-communities, while broad-spectrum insecticide spraying caused violent fluctuation to parameters of individual abundance, species richness, and diversity index of these sub-communities.5. Population dynamics of cotton bollwormPopulation density of the first generation cotton bollworm larvae in wheat field was surveyed for consecutive 12 years by sampling with sweep net. Cotton bollworm population increased rapidly when the cropping system was reforming to expend cotton production. At present cotton bollworm is the major pest in southern Xinjiang.The effects of transgenic Bt cotton to bollworm were studied with the method of nude-eye inspection. Bt cotton gave very effective control against cotton bollworm.The influencing effects of grain production systems on the population of second generation of cotton bollworm in cotton were studied. The multi-harvest system provided cotton a good protection against cotton bollworm due to the corn plants in this system strongly attracted cotton bollworm adults when they were ovipositing, therefore reduced the density of cotton bollworm in cotton, compared with ton-grain system..The life table of natural population of cotton bollworm in cotton was studied. The important factors that caused the death of second and third generation of cotton bollworm in cotton field were predacious natural enemies. Predacious and parasitic natural enemies had strong conjoint control effect to both second and third generation, therefore considerably reduced the population trend indices of cotton bollworm. This confirmed the importance of natural enemy conservation, and showed that predacious natural enemies should be employed primarily in cotton bollworm natural biological control. The important stages in which natural mortality occurred were egg, first instar and sixth instar larvae for second generation, first, fifth, and sixth instar larvae for third generation of cotton bollworm. -Measures safe to natural enemies should be applied particularly in these important stages if cotton bollworm need to be controlled artificially.6. Population dynamics of aphids in cottonPopulation dynamics of aphids in cotton were studied for 3 years. Along with the evolution of planting system, Aphis gossypii Glover became the important cotton pest, while other aphid species became the minor pests. Bt cotton had no negative influence to the occurrence of pest aphids in cotton.7. Population dynamics of pest mirids in cottonPopulation dynamics of pest mirids in cotton were studied for 3 years. Along with the evolution of planting system, Lygus pratensis L. increased and became the major cotton pest. Bt cotton had no negative influence to the occurrence of this pest.8. Population dynamics of cotton spider mitesPopulation dynamics of spider mites in cotton were studied for 3 years. Along with the evolution of planting system, Tetranychus spp. population decreased and became the minor cotton pest. Bt cotton had no negative influence to the occurrence of spider mites.9. Population dynamics of cotton thripsPopulation dynamics of Thrips tabaci L. in cotton were studied for 3 years. Along with the evolution of planting system, Thrips tabaci L. population still remained at high level as previous, and was the major cotton pest. Bt cotton had no negative influence to the occurrence of this pest.10. Population dynamics of arthropod natural enemies in cotton fieldPopulation dynamics of natural enemies in cotton field was studied with the method of nude-eye inspection. The most of the arthropod natural enemy were lady beetles, predacious hemipteran bugs, and spider, occupying a total percentage of 85%-93%. The proportion of individuals of these 3 natural enemy groups was strongly influenced by the occurrence degree of Aphis gossypii Glover. Bt cotton had no negative influence to the occurrence of natural enemies, while the spraying of broad-spectrum chemical insecticide caused in reduction in the natural enemy populations.Results in these studies lay a reliable theoretical foundation and provide some applied methods to cotton pest biological control through natural enemy conservation, cotton pest ecological control through ecological environment manipulation, bringing Bt cotton into cotton IPM system, and cotton SPM (Sustainable Pest Management).
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