Toxicity and binding analyses of Bacillus thuringiensis toxin Vip3A in Cry1Ac-resistant and -susceptible strains of Helicoverpa armigera (Hübner)

The Bacillus thuringiensis vegetative insecticidal protein, Vip3A, represents a new family of Bt toxin and is currently applied to commercial transgenic cotton. To determine whether the Cry1Ac-resistant Helicoverpa armigera is cross-resistant to Vip3Aa protein, insecticidal activities, proteolytic activations and binding properties of Vip3Aa toxin were investigated using Cry1Ac-susceptible (96S) and Cry1Ac-resistant H. armigera strain (Cry1Ac-R). The toxicity of Vip3Aa in Cry1Ac-R slightly reduced compared with 96S, the resistance ratio was only 1.7-fold. The digestion rate of full-length Vip3Aa by gut juice extracts from 96S was little faster than that from Cry1Ac-R. Surface plasmon resonance (SPR) showed there was no significant difference between the binding affinity of Vip3Aa and BBMVs between 96S and Cry1Ac-R strains, and there was no significant competitive binding between Vip3Aa and Cry1Ac in susceptible or resistant strains. So there had little cross-resistance between Vip3Aa and Cry1Ac, Vip3A+Cry proteins maybe the suitable pyramid strategy to control H. armigera in China in the future.