Bollworms Not Evolving

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Bollworms are not evolving, reports New Scientist , 29 October 2005. Scientists are surprised to find that pink bollworms, a pest that destroys cotton crops, are not evolving resistance to the Bt toxin in genetically modified cotton. According to New Scientist, "It was expected that the pest would have evolved resistance to a toxin produced by GM cotton in as little as three years." Over the past eight years University of Arizona entomologist Bruce Tabashnik has been testing an average of 2,500 bollworm larvae each year from up to 17 different cotton fields and found only 1 in 50,000 had a resistance gene. Furthermore, the resistance gene only gave partial resistance, and the larvae that carried it did not thrive as well as the non-resistant larvae when they ate unmodified cotton.

Editorial Comment: Scientists assumed that bollworms would rapidly become resistant to Bt toxin because other insect pests have rapidly become resistant to other insecticides. However the reason for rapid rise in resistance to other chemicals is that some of the other insects already had resistance to these chemicals, and the application of them simply killed off the non-resistant insects, allowing the resistant ones to flourish. This is selection of already existing resistance; it is not evolution. Therefore it follows that if no resistance pre-existed in bollworms, a change of environment will not make it happen. (Ref. prediction, survival, genetics)

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