Proceedings of the National Academy of Sciences of the United States of America (2009) 106, 11889-11894

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Bruce E. Tabashnik, Gopalan C. Unnithan, Luke Masson, David W. Crowder, Xianchun Li and Yves Carrière (2009)
Asymmetrical cross-resistance between Bacillus thuringiensis toxins Cry1Ac and Cry2Ab in pink bollworm
Proceedings of the National Academy of Sciences of the United States of America 106 (29), 11889-11894
Abstract: Transgenic crops producing Bacillus thuringiensis (Bt) toxins kill some key insect pests and can reduce reliance on insecticide sprays. Sustainable use of such crops requires methods for delaying evolution of resistance by pests. To thwart pest resistance, some transgenic crops produce 2 different Bt toxins targeting the same pest. This 'pyramid' strategy is expected to work best when selection for resistance to 1 toxin does not cause cross-resistance to the other toxin. The most widely used pyramid is transgenic cotton producing Bt toxins Cry1Ac and Cry2Ab. Cross-resistance between these toxins was presumed unlikely because they bind to different larval midgut target sites. Previous results showed that laboratory selection with Cry1Ac caused little or no cross-resistance to Cry2A toxins in pink bollworm (Pectinophora gossypiella), a major cotton pest. We show here, however, that laboratory selection of pink bollworm with Cry2Ab caused up to 420-fold cross-resistance to Cry1Ac as well as 240-fold resistance to Cry2Ab. Inheritance of resistance to high concentrations of Cry2Ab was recessive. Larvae from a laboratory strain resistant to Cry1Ac and Cry2Ab in diet bioassays survived on cotton bolls producing only Cry1Ac, but not on cotton bolls producing both toxins. Thus, the asymmetrical cross-resistance seen here does not threaten the efficacy of pyramided Bt cotton against pink bollworm. Nonetheless, the results here and previous evidence indicate that cross-resistance occurs between Cry1Ac and Cry2Ab in some key cotton pests. Incorporating the potential effects of such cross-resistance in resistance management plans may help to sustain the efficacy of pyramided Bt crops.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Full text of article
Database assignments for author(s): Bruce E. Tabashnik, Yves Carriere, David W. Crowder

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
resistance/tolerance/defence of host

Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.

Pectinophora gossypiella Cotton (Gossypium)
Bacillus thuringiensis genes in crops (entomopathogen) Pectinophora gossypiella Cotton (Gossypium)
Bacillus thuringiensis Cry1A-toxin (entomopathogen) Pectinophora gossypiella Cotton (Gossypium)
Bacillus thuringiensis Cry2A-toxin (entomopathogen) Pectinophora gossypiella Cotton (Gossypium)