Field Abundances of Insect Predators and Insect Pests on Δ-endotoxin-producing Transgenic Cotton in Northern China

China is one of the largest producers of cotton in the world. Insect pests such as cotton bollworm, cotton aphid, and mirids are the major factors that contribute to a decrease in cotton production. Transgenic cotton that expresses a gene derived from the bacterium Bacillus thuringiensis (Bt) has been deployed for combating cotton bollworm since 1997 in China, and expanded rapidly to 3.7 million of the total cotton acreage of 5.3 million ha in 2004. Field monitoring on the change of pest status derived from Bt cotton commercialization in a large scale were conducted during 1998-2004 in Hebei Province. The results indicated that Bt cotton efficiently controls cotton bollworms, while the decrease of pesticide applications allows the build up of high populations of predators, such as lady beetles Coccinella septempunctata, lacewings Chrysopa sinica, spiders and others in mid-season. Furthermore, planting Bt cotton efficiently prevented the resurgence of cotton aphids caused by insecticide use for control of cotton bollworm. However, the investigation of the seasonal dynamics of mixed populations of mirids showed that mirid density increased drastically, probably due to a reduction in the number of foliar insecticide applications in Bt cotton fields.