Development of resistance against Cry toxins from Bacillus thuringiensis (Bt) is one of the main concerns in the use of transgenic Bt plants. The use of combinations of Cry toxins in Bt transgenic crops or gene stacking, has been proposed as a strategy to delay resistance. For this, very different toxins with distinct modes of action should be selected. In the case of Bt cotton simultaneous expression of Cry1Ac and Cry2Aa has been proposed to delay resistance in Heliothis virescens (tobacco budworm). However, the CXC and KCBhyb Cry1Ac–selected laboratory strains of H. virescens developed high levels of cross-resistance to Cry1Aa, Cry1Ab and Cry2Aa, suggesting that this insect can develop cross-resistance to similar but also very different toxins. In specific toxin binding and binding competition experiments only Cry1Aa binding was affected in both resistant strains, while binding and insertion of Cry1Ac was unaffected when compared to susceptible insects. Since Cry1Aa and Cry2Aa do not share binding proteins in H. virescens, an additional mechanism for resistance against Cry1Ac and Cry2Aa should be present in these insects. Our results suggest simultaneous occurrence of at least two mechanisms of resistance in CXC and KCBhyb insects, and questions the effectivity of gene stacking to delay development of resistance.
Species 1: Lepidoptera Noctuidae Heliothis virescens (Tobacco budworm)
Keywords: Bacillus thuringiensis, resistance
Back to Student Competition Display Presentations, Subsection Ce. Insect Pathology and Microbial Control
Back to Student Competition Poster
Back to The 2002 ESA Annual Meeting and Exhibition