Genesis of Eden

Genesis Home

Pests with a purpose.
Why farmers must offer refuge to their worst enemies New Scientist 21 Feb 98

COMPANIES selling crops that have been genetically engineered to make their own pesticide must take steps to stop insects developing resistance to the poison, an expert panel told the US Environmental Protection Agency last week. The panel warned that unless the EPA forced companies to take action, the pesticide could quickly become worthless. But it failed to agree on exactly how companies and farmers might tackle the problem. This year is the third in which farmers in the US have been able to grow crops that manufacture the Bt toxin, a natural poison "borrowed" from the soil bacterium Bacillus thuringiensis. Even organic farmers approve of Bt-crops because the toxin is highly specific, killing particular pests without harming other animals, and it does not build up in the environment. Opponents, including entomologists, argue that because the plants produce the pesticide continuously, there is a risk that pests will develop resistance to it. The main strategy for trying to prevent this is to set aside "pest refuges-, areas planted with unaltered crops that do not produce Bt. The idea is that any surviving pests in the Bt fields wfll mate with the non-resistant pests from the refuges, diluting the pool of resistance genes. The EPA already insists that when farmers grow Bt cotton 4 per cent of their c-op must be unaltered cotton that is not treated with any pesticide. If they need to spray with other pesticides, then 20 per cent of their crop must be non-Bt cotton. Critics believe that these refuges are too small. In a report prepared for the Union of Concerned Scientists (UCS), a pressure group based in Washington DC, six entomologists recommended doubling or tripling the size of the refuges. They also want the unaltered crop planted alongside engineered crops. They are worried that if farmers plant their non-Bt plants miles from their Bt fields, the resistant insects and the suscepfible ones will never mate. The expert panel failed to make specific recommendations, arguing that no one knows enough about resistance to prescribe specific measures. The ideal refuge size will depend on the type of crop, the weather and pests in the region where it is grown, it said. Critics had wanted strict controls. "Long-term resistance management won't matter a hoot if we lose Bt in the short term," says Jane Rissler, a scientist with the UCS. Kurt Kleiner, Washington DC