Transgenic cotton coexpressing Vip3A and Cry1Ac has a broad insecticidal spectrum against lepidopteran pests

Although farmers in China have grown transgenic Bt-CrylAc cotton to resist the major pest Helicoverpa armigera since 1997 with great success, many secondary lepidopteran pests that are tolerant to CrylAc are now reported to cause considerable economic damage. Vip3AcAa, a chimeric protein with the N-terminal part of Vip3Ac and the C-terminal part of Vip3Aa, has a broad insecticidal spectrum against lepidopteran pests and has no cross resistance to CrylAc. In the present study, we tested insecticidal activities of Vip3AcAa against Spodoptera litura, Spodoptera exigua, and Agrotis ipsilon, which are relatively tolerant to CrylAc proteins. The bioassay results showed that insecticidal activities of Vip3AcAa against these three pests are superior to CrylAc, and after an activation pretreatment, Vip3AcAa retained insecticidal activity against S. litura, S. exigua and A. ipsilon that was similar to the unprocessed protein. The putative receptor for this chimeric protein in the brush border membrane vesicle (BBMV) in the three pests was also identified using biotinylated Vip3AcAa toxin. To broaden Bt cotton activity against a wider spectrum of pests, we introduced the vip3AcAa and clylAc genes into cotton. Larval mortality rates for S. litura, A. ipsilon and S. exigua that had fed on this new cotton increased significantly compared with larvae fed on non-Bt cotton and Bt-CrylAc cotton in a laboratory experiment. These results suggested that the Vip3AcAa protein is an excellent option for a "pyramid" strategy for integrated pest management in China.