Next-Generation Transgenic Cotton: Pyramiding RNAi with Bt Counters Insect Resistance.

Transgenic crops expressing Bacillus thuringiensis (Bt) toxins have become a cornerstone in integrated pest management. To counter rapidly increasing pest resistance to transgenic crops producing single Bt toxins, transgenic plant "pyramids" producing two or more Bt toxins targeting the same pest have been widely adopted. However, cross-resistance and antagonism between Bt toxins limit the sustainability of this approach. Here we describe a new type of pyramid combining protection from a Bt toxin and RNA interference (RNAi). We developed and tested transgenic cotton plants producing both Bt toxin Cry1Ac and double-stranded RNA from the global pest Helicoverpa armigera that interferes with its synthesis of juvenile hormone. We discovered that no cross-resistance occurred between these two traits, and they acted independently against a susceptible strain of H. armigera. Computer modeling predicts that if large refuges of non-transgenic host plants are present, pyramided cotton combining Bt and RNAi could delay resistance by 14 to 75 years relative to using Bt cotton alone.