| A systematic survey was made in transgenic Bt cotton fields(with the IPM and the Chemical control cotton field of transgenic Bt cotton), routine cotton field and surrounding habitat (non-crop habitat) of cotton fields in Nanpi county, Hebei province, from 2001 to 2002.And arthropod biodiversity of different cotton fields, resistance of Bt cotton, and dynamics of arthropods population of surrounding habitat were studied in lab. The main results showed as follows:1. 147 species of arthropods in 69 families of 17 order were found in cotton fields. Among them, 61species in 32 families belonged to pests; 17 species in 10 families belonged to neutral arthropods; 69 species in 34 families belonged to natural enemies. The natural enemies included 6 species of ladybirds, 26 species of spiders in 11 families, 5 species predatory bugs in 5 families, 3 species of green lacewings, 18 species of parasitoids wasp in 9 families and 11 species of other natural enemies of 7 families.2. Analysis showed that there was no significant difference between transgenic Bt cotton fields and routine cotton field in diversity, dominance, evenness and abundance of species, functional groups, sub-community and community. However, in the cotton field with the IPM, diversity and evenness were increased and dominance was decreased significantly. Abundance of pest sub-community was also decreased, while Abundance of neutral and natural enemies sub-community was increased remarkably. Population multiplying and community reestablishing of arthropod in cotton fields mainly happen in July. And at the same time , in the cotton fields with the IPM and decreasing farm insecticide, the control efficiency of natural enemies would be improved significantly, and which resistance of Bt cotton become weak was minimized.Tthe stability of cotton eco-system was increased.3.Servey indicated that there was much natural enemies in surrounding habitat (non-crop habitat) of the cotton fields, such as wheat fields, weeds, corn fields. They immigrated into cotton fields from the surrounding habitat, which played the role as a Species pool of natural enemies, from the last ten-day period of May to the beginning of June. They raised their proportion to pest and control role.Limited by habitat, a large number of natural enemies emigrated cotton fields late June. From early July to late August, with aphids in cotton fields multiplying rapidly, natural enemies moved in from other habitat, such as spring corn fields, weeds, jujube trees. And then population began to recovery and community began to reestablish. After middleAugust, predators kept a stable population dynamics since the number of Thrips tabaci Lindeman, Bemisia tabaci Gennadius, Empoasca biguttula Ishida induced while the number of Aphis gossypii Glover reduced.4. The study of resistance of transgenic Bt cotton showed that there was no signifycant effect on the number of cotton bollworm eggs. The number of the rest bollworm larvae of each generation of Bt cotton field was significantly lower than that of routine cotton fields. Damages on all organs of 2nd, 3rd and 4th generation cotton were less than the control fields and the difference was also significant, which showed that transgenic Bt cotton has marked efficiency on controlling bollworm. However, because of the varied efficiency of transgenic Bt cotton due to different time and organs, it was effective to 2nd generation bollworm. As to 3rd and 4th generation bollworm, it is necessary to use chemical control 3-4 times. Another practical way was to release Trichogramma chilonis which could not only reduced bollworm eggs and made up the loss caused by the weak resistance, but cut down using of farm insecticide and protected natural enemies.5. Survey showed that Lygus lucorum Mayer-Diirhas 3 generations a year. The first generation moved in cotton field where they completed the other two generations. At the last ten-day period of September they lay eggs that live through the winter on cotton, weeds, dead leaves and branches of trees ectl... |
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