Composition of Pests and Natural Enemies and Dynamics of Dominant Groups in Transgenic Bt Cotton Fields

In order to study the influence of transgenic Bt (Bacillus thuringiensis) cotton on the structure of arthropod community and the dominant groups in Yangtze River Valley, a system survey was conducted in Nanjing, Jiangsu Province, in 2002. Three transgenic Bt cotton varieties (Sukang 103, GK22 and sGK321) and one common cotton variety (Simian 3) were adopted. The component species in transgenic and common cotton fields were similar. But there was a little difference in the individual numbers of some special species. The dominant pests in transgenic cotton fields were aphids (Aphis gossypii Glover), cotton whitefly (Bemisia tabaci Gennadius) and leafhopper (Empoasca biguttula Ishida) , whereas aphids, cotton leafroller (Sylepta derogata Fabricius) were the dominant pests in common cotton fields. Ladybugs (Propylaea japonica Thunberg) , green lacewings (Chrysopa sep-tempunctata Wesmael) , and spiders (Misumeenops tricuspidatus Fabticius) were the dominant species of natural enemies in all of cotton fields. Based on their trophic relationships and taxonomy relationship, the field arthropods including pest groups, natural enemy groups and neutral arthropods were divided into four nutrient classes, six guilds and 26 groups. The phytophagous class is the dominant class in the four nutrient classes, following by the predacious class. In the phytophagous class, sucking pests takes the first place in abundance, in both Bt-cotton and common cotton fields. In the predacious groups, ladybuds, spiders and lacewings are the major natural enemy groups. The dynamics of the major pest groups and natural enemy groups were displayed following the sampling times se- quence, which was with the growth of cotton plants. The biggest difference between the Bt cotton and common cotton fields is the population of caterpillar, which is significantly lower than the later, for the good control of Bt cotton on target pests. While there is little difference for the sucking pest groups and the natural enemies between the Bt cotton and common cotton fields. These results indicated that transgenic Bt cotton could depress the population of caterpillar, but had little effect on the natural enemies.