The Structure And Dynamics Of Natural Enemy Community And Its Controlling Effect Against The Cotton Aphids (Aphis Gossypii Glover) In Cotton-Alfalfa Intercrop Field

The study was carried out with a view to the production of the cotton and the control of the Aphis gossypii Glover. By field systematic investigation, the natural enemy community structure and dynamics, numeric dynamics of the dominant pests and natural enemies, the function response of the dominant natural enemies to Aphis gossypii Glover and the crop yields and output value were investigated in cotton fields in which the cotton and the alfalfa were planted according to various ways in Dunhuang in 2005. The theoretical foundation was provided for IPM of pests and the increase of the output value in cotton fields. The research contents and results were listed as follows:(1) The investigation of the natural enemy community structure. 23 species of natural enemies were collected and identified, in which 20 species belonging to 12 families, 5 orders were insects and 3 species belonged to 3 families of Arachnida. Ladybirds, spiders, lacewings and flower bugs were dominant natural enemies. Habitat and reproduction place were provided for the natural enemies by planting alfalfa, which increased significantly the species and quantity of the natural enemies. In the cotton-alfalfa intercrop fields (75cm-wide and 50cm-wide alfalfa every other film), there were the most species and the largest number of the natural enemy.(2) The dynamics of the natural enemy community was studied. In the cotton-alfalfa intercrop fields, quantity and species of the natural enemies and diversity index of the natural enemy community were affected greatly when the alfalfa was cradled. The effect was determined by planting manner of the alfalfa in cottons, of which 75cm-wide and 50cm-wide alfalfa every other film had the best effect.(3) Analysis of the temporal niche breadths and overlaps of the cotton aphid and the dominant natural enemies in cotton fields.The results showed the temporal niche breadths of ladybirds, spiders and lacewings were smaller in cotton-alfalfa intercrop fields than the control cotton field and the temporal niche overlaps index of the enemies vs the Aphis gossypii Glover was higher. Our results indicated that cradleding the alfalfa resulted a sharp increase of the natural enemies and a better synchronization of the the enemies vs the cotton aphids.Thus, the cotton-alfalfa intercrop fields had a better effect on controlling the cotton aphid.The temporal niche breadth of the Aphis gossypii Glover was the largest in the control cotton field, and the temporal niche breadth was the smallest in cotton-alfalfa intercrop fields (75cm-wide alfalfa every other film). Although there were two peaks of the Aphis gossypii Glover before cradling, the Aphis gossypii Glover was controlled effectively and the number of...