| College of Plant Protection, QinQiujuThe occurances of cotton bollworm and their predators were investigated on the transgenic Bt cotton in 1999 and 2000 in Agricultural university of Hebei. Some conventional insecticides were bioassayed by topical application against strains of Helicoverpa armigera(Hubner) collected from field crops in Hebei province in china during the 2000 and 2001 growing season..The investigation showed that the egg numbers of cotton bollworm were similar in all cotton fields, but the numbers of the second and third generation Larvae on transgenic Bt conttons were much lower than those on common cotton. There is no diffrence of predator in all fields.Topical application bioassays on third instars showed susceptible to middle resistance to conventional Organophosphorus in all sites, 6.6 to 17.5 fold resistance to monocrotophos, 6.1 to 22.5 fold resistance to methamidophos, 5.1 to 10.4 fold resistance to phoxim, 2.9 to 6.8 fold resistance to methy parathion. 1.5 to 5.7 fold to isocarbophos; 96.6 to 331.0 fold to cypermethrin; 42.3 to 114.5 fold to delamethrin; 13.0 to 23.5 fold to high effect cypermethrin and susceptible to methomyl, Compared with 1995, the resistance levels of all kinds of insecticides were much lower.It is suggested that those insecticides such as isocarbophos, methomyl in all sites and phoxim in Baoding, Nanpi, Gucheng still can be uesed; phoxim uses in Julu district and high effect cypermethrin in all sites should be limited. Pest forcasting and insecticide resistance monitoring programes should be encouraged. IPM should be used on transgenic Bt contton and proprate chemical control programe also needed when necessary.This studies tested the effects of transgenic Bt cotton on the cotton bollworm and their natural enemies, bioassays were also made against strains of cotton bollworm to conventional insecticides, which can provide strategies for pest control and transgenic Bt36cotton management. |
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