No Increase in Resistance Seen for Pink Bollworm Populations
Genetically engineered cotton in Arizona, grown using a strategy mandated by the EPA, is effectively controlling a common crop pest without causing increased pesticide resistance, suggesting that
transgenic crops could help the environment through reduced insecticide use. Researcher Yves Carriere, an evolutionary ecologist at the University of Arizona in Tucson, believes that "Transgenic crops have potential to improve agriculture, but we must be careful when we use them." To minimize the risk of evolved resistance against Bt crops, the EPA in 1995 required all growers of Bt cotton to plant crops that do not generate the toxins alongside Bt crops. Insects vulnerable to Bt toxins are kept alive in such fields to mix their insecticide-susceptible genes with resistance traits to dilute and therefore delay the evolution of resistance among their descendants. "The EPA was right in doing so," Carriere explained. "This refuge strategy is absolutely needed to delay the evolution of resistance." Carriere and colleagues looked at the population density of pink bollworm, a key cotton pest, across 300,000 acres of cotton in Arizona over a 10-year span - five years before Bt cotton was deployed and five years after. More than 1,000 traps containing sex pheromones were deployed to capture insects for study. Investigators found up to a four-fold decrease in pesticide applications following the introduction of Bt cotton, which also led to up to six-fold decrease in pink bollworm population density. This steady decline suggests the pink bollworm soon could be eliminated as a key pest.
A senior staff scientist for the Union of Concerned Scientists in Washington, was pleased to see the results. "The Arizona scientists deserve a lot of credit for their systematic study of the use of Bt cotton," she said. "Frankly, this is what we'd like to see in many other places in the country." Both groups feel these results do not necessarily extrapolate to Bt crops in other parts of the country. Says Carriere, "Here in Arizona it is clear Bt cotton has caused a dramatic reduction in the use of synthetic insecticides. But I'm talking about Arizona. This is not my general position for every transgenic." (UPI, 2/4/03 via AgNet).
