| Cotton spider mites are the most destructive herbivorous arthropods (Arachnida, Acari, Tetranychidae) of about113host plants, such as cotton, Gossypium hirsutum L. eggplant and weeds in the world. The group is composed of5dominant species in China, namely Tetranychus cinnabarinus Boisduval, T. truncates Ehara, T. urticae Koch, T. turkestani Ugarov et Nikoskil, T. dunhuangensis Wang.Jingzhou city is a typical wetland agricultural area adjacent to Yangtze River and Han River. It is easy and common practice for land owners to use their land interchangeably as intensive culture ponds, cotton fields or rice paddy fields. The use of the land is often determined by changes in the market price of fish, cotton or rice paddy as well as the incidence of fish disease. In recent years, along with the time and area planted with transgenic-Bt cotton in Jingzhou city increases so does the damage caused by cotton spider mites. Although chemical control plays also an important role in controlling cotton spider mite, it is easy to caused "3R" problem.The study was conducted between April2011to October2011in the Yangtze River middle reaches district (Jingzhou City, Hubei Province), China. Distribution of cotton spider mites on host plants on cotton field ridge in winter and spring, effect of the transfer Bt gene cotton, the plant of cotton after the fish pond and paddy-cotton crop rotation on abundance of cotton spider mites and total phenolic content of leaves and their relationship were investigated. The main results were as follows:1) Distribution of cotton spider mites on host plants on cotton fields ridge in winter and spring Distribution of cotton spider mites in the winter and spring on host plants of the15kinds of cotton fields ridge from the4planting cotton districts in the middle reaches of the Yangtze River, including Ruichang of Jiangxi Province, Li County of Hunan Province, Jingzhou County of Hubei Province, Jiangbei Farm of Hubei Province, were surveyed by equidistant sampling method. The results showed that there were64host plants species,27families in cotton fields, Veronica polita Fries. Cayratia japonica Gagnep and Youngia japonica DC were dominance host plants species of cotton spider mites in the winter and spring among them. The ratio of the number of the adults and nymphs, larvae and eggs of cotton spider mites on host plants in the winter and spring were72.1:20.5:7.4. the adults and nymphs were the largest number among them. Cotton spider mites in the winter and spring on host plants of the cotton fields ridge of the type of Wheat-cotton. in previous wheat fields sprayed with herbicides, was the least amount among5types, there was only3.3%host plants fed by cotton spider mites. It was no significant effect on the number of cotton spider mites on host plants of the cotton field ridge in the winter and spring by transforming the pond into the cotton fields or by transforming the rice fields into the cotton fields.2) Effect of low-lying land environment on abundance of cotton spider mites and total phenolic content of leaves and their relationship The possible advantage of cotton production established in low-lying land area over intensive culture pond was systematically investigated by comparing the abundance of cotton spider mites on these plants to that in conventional production areas at the Jiangbei farm, Hubei Province, China. Cotton fields (Ezamian No.24F1) recently grown at low-lying land area supported significantly lower populations of cotton spider mites than conventional long established cotton fields. There were no significant differences in mite populations between cotton fields established in low-lying land area in the current year or1or2years earlier. The pest control advantage provided by pond areas was present whether or not acaricides were used. The total phenolic content of cotton leaves differed occasionally between treatments but did not seem to have affected the abundance of mites. The number of eggs, larva-nymph-adults, egg-larva-nymph-adults, the percentage of host plants colonized by cotton spider mites and the plant damage index were independent of the total phenolic content in leaves. The results are discussed in relation to integrated pest management and the mineral balance hypothesis.3) Effect of transgenic Bt cotton on abundance of cotton spider mites and total phenolic content of leaves and their relationship The differences of percentage of cotton plants infested with cotton spider mites between in transgenic Bt and in non-transgenic Bt cotton plots were investigated in Tai Lake farm, Hubei Province, China. In acaricide treated plots, transgenic Bt cotton does not result in a change of the abundance of cotton spider mites compared to that in non-transgenic Bt cotton, however, without acaricide treated plots, transgenic Bt cotton significantly increases the abundance of cotton spider mites compared to those of non-transgenic Bt cotton. The number of eggs, larva-nymph-adults, egg-larva-nymph-adults and the plant damage index are independent of the total phenolic content in leaves. The results are also discussed in relation to integrated pest management. It was very necessary for a nontarget cotton spider mites of transgenic Bt cotton fields to control in wetland agricultural area.5) Effect of Cotton Production over Paddy Land on Abundance of Cotton Spider Mites and Total Phenolic Content of Leaves and their Relationship The differences of the abundance of cotton spider mites was systematically investigated among the different treated transgenic Bt (Ezamian No.24F1, Ek9-parental line of Ezamian No.24F1) production over paddy land at the Tai lake farm, Hubei Province, China, over the period13May and13September2012. Cotton fields in the current year or1year earlier established in paddy areas supported significantly lower populations of cotton spider mites than2years earlier established cotton fields. The total phenolic content of cotton leaves differed occasionally between treatments but did not seem to have affected the abundance of mites. The number of eggs, larva-nymph-adults, egg-larva-nymph-adults, the percentage of host plants colonized by cotton spider mites and the plant damage index were independent of the total phenolic content in leaves. One can only speculate on the most likely factor(s) responsible for the lower abundance of spider mites in cotton fields grown paddy land area would be humidity. In agricultural irrigation facilities area, the promotion of paddy-cotton crop rotation model can effectively reduce abundance of spider mites in cotton fields grown paddy land area. The interference effect of rain on abundance of cotton spider mites The influence of heavy rainfall on abundance of cotton spider mites and correlation between the height of the cotton plant, mud level of cotton leaf and the decline rate of cotton spider mites were systematically investigated in Yangtze University. The results showed that heavy rainfall has the same obvious effect to abundance of cotton spider mites regardless of the cotton leaf mites in any position such as decline rate of upper (85.9±4.5%), middle (98.3±1.3%) and down (99.68±0.3%) of cotton plant. The total decline rate was94.6±1.7%. The decline rate of cotton spider mites in upper of the cotton plant leaf was respectively significantly lower than in the middle and lower. After the heavy rainfall, there was significantly negative correlation between the height of the cotton plant and the decline rate of cotton spider mites, and a positive correlation very significantly between the mud level of cotton leaf and the decline rate of cotton spider mites.In a word, through this project research, the purpose is to provide theoretical basis on the prevention and non-chemical control to cotton spider mites in the region. |
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