Jian-Zhou Zhao1, Jun Cao2, Yaxin Li1, Hilda L Collins1, Richard T Roush3, 4, Elizabeth D Earle2
& Anthony M Shelton1
1
Department of Entomology, Cornell University/NYSAES, 630 W. North Street, Geneva, New York 14456, USA.
2
Department of Plant Breeding, 514 Bradfield Hall, Cornell University, Ithaca, New York 14853, USA.
3
Department of Applied and Molecular Ecology, Waite Institute, University of Adelaide, Glen Osmond 5064, Australia.
4
Present address: Statewide IPM Program, University of California, 1 Shields Ave., Davis, California 95616-8621, USA.
Correspondence should be addressed to Anthony M Shelton ams5@cornell.edu
Preventing insect pests from developing resistance to Bacillus thuringiensis (Bt) toxins produced by transgenic crops is a major challenge for agriculture. Theoretical models suggest that plants containing two dissimilar Bt toxin genes ('pyramided' plants) have the potential to delay resistance more effectively than single-toxin plants used sequentially or in mosaics. To test these predictions, we developed a unique model system consisting of Bt transgenic broccoli plants and the diamondback moth, Plutella xylostella. We conducted a greenhouse study using an artificial population of diamondback moths carrying genes for resistance to the Bt toxins Cry1Ac and Cry1C at frequencies of about 0.10 and 0.20, respectively. After 24 generations of selection, resistance to pyramided two-gene plants was significantly delayed as compared with resistance to single-gene plants deployed in mosaics, and to Cry1Ac toxin when it was the first used in a sequence. These results have important implications for the development and regulation of transgenic insecticidal plants.
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