15 Apr 2013, BioSpectrum Bureau , BioSpectrum
Singapore: Entomologists from University of Arizona (UA), US, have discovered that the popular strategy of planting multi-toxin producing genetically modified crops, to prevent pests from quickly adapting to crop-protecting toxins, may fail in some cases unless better preventive actions are taken. The research has been published in the Proceedings of the National Academy of Sciences.
Dr Yves Carrière, professor of entomology, college of agriculture and life sciences, UA, who led the study, said that, although Bt crops have helped to reduce insecticide sprays, boost crop yields and increase farmer profits, their benefits will be short-lived if pests adapt rapidly.
Dr Bruce Tabashnik, a co-author of the study and head of the UA department of entomology, said that, "Our goal is to understand how insects evolve resistance so we can develop and implement more sustainable, environmentally friendly pest management."
Bacillus Thuriengensis (Bt) crops were first grown widely in 1996, and several pests have already become resistant to plants that produce a single Bt toxin. In order to thwart further evolution of pest resistance to Bt crops, farmers have recently shifted to the 'pyramid' strategy, in which each plant produces two or more toxins that kill the same pest. One critical assumption of the pyramid strategy is that the crops provide redundant killing.
However, in the real world, things are a bit more complicated. If the assumption of redundant killing is correct, caterpillars resistant to the first toxin should survive on one-toxin plants, but not on two-toxin plants, because the second toxin should kill them, Carrière explained. But on the two-toxin plants, the caterpillars selected for resistance to one toxin survived significantly better than caterpillars from a susceptible strain. These findings show that the crucial assumption of redundant killing does not apply in this case and may also explain the reports indicating some field populations of cotton bollworm rapidly evolved resistance to both toxins.