Resistance management is critical for the sustainable use of transgenic plants expressing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt). Theoretical models suggested that plants containing two dissimilar Bt toxin genes in the same plant have the potential to delay resistance much more effectively than single toxin plants used sequentially or in mosaics. We used a unique model system that is composed of Bt transgenic broccoli plants and different resistant strains of the diamondback moth (Plutella xylostella) to test if the resistance to both toxins will develop faster or slower when subjected to plants that express both toxins simultaneously, in mosaics, or sequentially. A synthetic population of the diamondback moth that contains genes for resistance to Cry1A at a frequency of 0.03 and to Cry1C at 0.10 was used in a greenhouse cage study. After 18 generations the allele frequency of Cry1Ac resistance was >0.5 in all replicates of the mosaic treatment and the sequential treatment (Cry1Ac plants first). The allele frequency of Cry1C resistance was also > 0.5 in one of the four replicates of the mosaic treatment. In the cages with pyramided two-gene plants, the mean allele frequency was 0.22 for Cry1Ac-resistance and 0.07 for Cry1C-resistance. Insect population densities displayed similar trends with the pyramided plants providing the best control. These results indicated that, compared to sequential or mosaic deployment of Bt toxins in plants, pyramided two-gene plants could significantly delay resistance development to each or both toxins while providing control of the pest population.
Species 1: Lepidoptera Plutellidae Plutella xylostella (Diamondback moth)
Keywords: Bacillus thuringiensis, Resistance
Back to Ten-Minute Papers, Subsection Fa. Host Plant Resistance and F. Crop Protection Entomology
Back to Ten-Minute Papers, Section F. Crop Protection Entomology, Subsections Fa and Fb
Back to The 2002 ESA Annual Meeting and Exhibition