Background
Transgenic maize expressing toxins derived from the bacterium Bacillus thuringiensis (Bt) may be commercially planted in northern China where Bt cotton has been planted for more than two decades. While Bt maize brings additional benefits for insect control, it complicates the resistance management of cotton bollworm (CBW), Helicoverpa armigera (Lepidoptera, Noctuidae), a common target of Bt cotton and Bt maize.
Results
We used a two-locus population genetic model to assess the risk of resistance in CBW when Bt cotton and Bt maize are planted concurrently. Results of model simulations showed that planting Bt maize together with Bt cotton significantly increases the risk of resistance if Bt cotton and Bt maize share a similar Bt toxin. The risk of resistance is higher in the case of one-toxin Bt maize than in the case of two-toxin Bt maize. Parameters associated with the preexisting resistance in CBW all could impact on the risk of resistance but with different extents. Among them, the most notable ones are the dominance of resistance and fitness cost, which can dramatically affect the risk of resistance, especially when the proportion of natural refuges is reduced.
Conclusions
We concluded that the preexisting resistance in CBW to Bt cotton can significantly increase the risk of resistance when Bt maize and Bt cotton are planted concurrently and that using two-toxin Bt cotton and maize instead of one-toxin ones are needed in order to reduce the risk of resistance.