Modified toxin helps crops kill resistant insects

A modified form of a commonly used pesticide may one day provide farmers with a new weapon against the development of **resistance** among insect pests. #img_768#.<> *Pink bollworm moths: a pest for cotton. (Alex Yelich, University of Arizona)* The new compound is a modified version of the 'Bt' toxins — a class of chemicals that specifically target caterpillars and are naturally produced by the bacterium *Bacillus thuringiensis*. Farmers have long used Bt sprays to protect their crops, and cotton and corn engineered to make the toxin themselves have been grown for more than a decade. But, using plants that continuously produce the toxin has the potential to accelerate the emergence of Bt-resistant insects. "It’s almost inevitable that there will be more **resistance** to Bt toxins now that they’re being used much more widely," says Bruce Tabashnik, an entomologist at the University of Arizona in Tucson, and a member of the research team. ** Resist the resistance** Now, researchers from the National Autonomous University of Mexico in Morelos have designed a new way to stave off pests by modifying the Bt toxins so that they resist insect **resistance**. They found that when they deleted a specific region of a Bt toxin, the toxin no longer needed to bind to a receptor before it could kill its host. They tested two versions of the new toxin against Bt-resistant pink bollworms (Pectinophora gossypiella ) reared in the lab. The bollworms were at least a hundred times more susceptible to one form of the modified Bt toxin than to the natural compound, the researchers report in "Science":[ http://science.com]. The modified toxin will probably require more evaluation to ensure its safety in humans. If the toxin passes those tests, we’ll have a new way to proceed, say the researchers. Source: "http://www.nature.com":[ http://www.nature.com/news/2007/071101/full/news.2007.211.html]

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