Toxin and control efficiency of transgenic Bt cotton against Helicoverpa armigera (Hubner) in Northern China

There were high toxins of Bt cotton to new emerged larvae and 1st instar larvae, the highest efficacy reached 90.5% after 72 hours in laboratory. The control sequences of Bt cotton to CBW emerged larvae>1st instar larvae>2nd instar larvae>3d instar larvae, tender leave>tip>square/flower>young boll, leave in 5-leaves stage>leave in square/flower stage, 2nd generation>3d generation>4th generation, separately. The transgenic Bt cotton strains of B_(2)、B_(3)、R_(2)、R_(3)、B_(4)、B_(6)、3、8、10、16、26、36 were identified to high resistance of grade I. The resistance of Bt cotton to cotton aphid presented different trends in its second generation with high efficacy to CBW and pink bollworm in field trial. The population of cotton leaf hoper and greenhouse whitefly in Bt cotton increased 53.6%-58.4%, 19.2%-67.4%, respectively, when parasitoids of CBW decreased 27.5%-56.1% sharply. The planting demonstration (more than 50 thousands hm~(2) accummulated acreage) in large scale in Yellow River cotton growing-area during 1995-1996, shows that the abilities of control efficacy of Bt cotton, the lint yield and guality of Bt cotton could meet needs of cotton grower and industrial in China.