Studies On Joint Action Of B.t. And Several Toxicants On Insects

Bacillus thuringiensis(B.t.) has been widely used because of its specificity for target insects, low development cost and environmental compatibility. This thesis aims at guiding a reasonable combination of B.t. and other biological insecticides and also introducing the practical combination technique of B.t. and other biological insecticides in the perspective of insect never toxication. The result is obtained by carrying out on the combination mechanism of B.t. and other newly developed biological insecticides, especially researches on the combinational functions of some animal and plant toxins, for example , Buthotoxin and Avermectin.The following is the main results of the research.(1) The susceptibility of larvae of less army worm Helicoverpa armigera to B.t. was increased when the larvae were fed with transgenic cotton compared to those fed on the non-transgenic cotton, but decreased after 10-generation's feeding with the bt transgenic cotton plants. Biochemical analysis showed that the activities of acetylcholinesterase and carboxylesterase were obviously higher in those larvae fed on the transgenic cotton.(2)Observation on the poisoning symptom showed that the poisoning of the insects treated with B.t.+ Buthotoxin, B.t.+ Avermectin, B.t.+ Nereistoxin and B.t.+ Azadirachtin mixture were enhanced and accelerated for about 24hrs..(3) Greenhouse tests indicated that joint treatment with B.t. and Nereistoxin, Avermectin, Buthotoxin and Azadirachtin presented better control effects than any single toxicant. The LC50 value of each mixture is 75.405mg/L,116.830 mg/L,20.110 mg/L,80.593mg/L5 27.992 mg/L respectively, and the C.T.C values of LC50 is 217.9, 254.8,1064.0, 443.4 and 1082.6 respectively.(4)Electrophysiological effects of the mixtures on the midgut never-muscle systemshowed synergistic symptoms. The frequency and amplitude of spontaneous action potentials was increased obviously. The average frequency and amplitude value caused by the joint treatment with B.t, and Buthotoxin is as follow: 0.9±0.08 times/second and 0.12±0.029mv before the treatment, 1.4±0.25 times/second and 0.18?.053mv at 1minute, 2.9±0.31 times/second and 0.31±0.032mv in 2 minutes . The value for the joint treatment B.t. and Avermectin is 0.8±0.10 times/second and 0.10±0.018mv before the treatment, 1.3±0.14 times/second and 0.15±0.017mv in 3minutes , 2.8± 0.31 times/second and 0.34±0.044mv in 6minutes . The value for the Joint treatment B.t. and Nereistoxin,. is 1.2±0.24 times/second and 0.14±0.029mv before the treatment , 0.8±0.09 times/second and 0.09±0.017mv in 5minutes , 2.2±0.17 times/second and 0.28±0.054mv in 8 minutes .For conclusion, the author believed that the synergistic mechanism of B.t and Bt-transgenic cotton relate to the acetylcholinesterase and carboxylesterase, and there existed different kinds of joint action between B.t. and many other toxicants, and which is useful in insect pest management, or resistant management of the transgenic cotton plants.