| Bacillus thuringiensis (Bt) is a spore-forming gram-positive bacterium. During sporulation, the intracellular insecticidal crystal proteins (Cry proteins) are produced as phase-bright inclusion. These proteins are toxic to insect larvae in the orders Lepidopetera, Duptera and Coleopteoptera. The Cry proteins from B. thuringiensis have been developed as one of the most successful biological agents in agriculture to control insect pests. The vegetative insecticidal proteins(VIPs) secreted outside the cells during mid-logarithmic growth were found recently. Two novel VIPs which are toxic to Helicoverpa armigera were identified from Bt-LS1 and Bt-LS8 isolates, respectively. The characteristics of Bt-LSl and Bt-LS8, the cloning and expression of VIP3A were reported in this study.Insecticidal activity of the isolates from Bt-LS1 and Bt-LS8 was assayed against H. armigera larvae and Bt var kurstaki strain (HD-1) was used as positive control in this experiment. The result from Cry proteins showed that LC50 of Bt-LS 1 and Bt-LS8 is 4.9 ×106 and 3.3 ×106 cells/mL respectively, which was strong for toxic to H.armigera larvae than HD-1 with LC50 of 2.8 ×107 cells/mL. The result from VIP showed that both Bt-LS1 and Bt-LS8 were highly toxic to H.armigera larvae with a mortality of 50.4%.In this study, screening of Bt strains containing vip3A genes and analysis of gene conservation were reported. vip3A genes of Bt isolates stored in our lab were identified using PCR amplification. The results showed that among 99 isolates, 55 contained this gene. On the basis of identification result, two isolates, Bt LS1 and Bt LS8 , highly toxic to Lepidoptera pests, were chosen and studied on location of vip3A. Results of location showed that plasmid DNA existing vip3A gene in LS1 and LS8 isolate, which vip3A gene successfully cloned in chapter Ⅲ different from other authors' identified on linear plasmids DNA.Two isolates, which were highly toxic to Lepidoptera pests, Bt-LS1 and Bt-LS8...
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