Biotech Cotton Not Detrimental to Biodiversity
Arizona farmers receive the same yield/acre, use fewer chemical insecticides and maintain insect biodiversity when they plant the biotech cotton known as Bt cotton, according to new research. The finding comes from the first large-scale study that simultaneously examined how growing Bt cotton affects yield, pesticide use, and biodiversity. “What we see is that it's positive here in Arizona - no doubt about it,” said Yves Carrièère, an associate professor of entomology at the University of Arizona in Tucson. “We've reduced pesticide use in Arizona. We've wanted to do that for 25 years.”
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Bt cotton has been genetically altered to produce Bt toxin, a naturally occurring insecticide that kills pink bollworm, a major pest of cotton. Bt cotton has been planted in Arizona since 1996. Now more than half of the state's 256,000 acres of cotton fields are planted with the biotech plants. Although it has eliminated the need for 5.4 conventional insecticide treatments (at a cost of $80/acre), some have suggested that in addition to killing the target pests, insecticide-containing crops like Bt cotton would also kill beneficial and non-target arthropods. The new study found that Bt cotton, also known as transgenic cotton, does not affect the biodiversity of insects in cotton fields. Carrièère said, “There were lots of factors that affected biodiversity in this study. Transgenics were not one of them.” He and his colleagues based their findings on a two-year study of 81 commercial cotton fields in a region of Arizona that spans about 2,500 square miles (6,600 square kilometers).
Bt cotton controls only one of Arizona's three major cotton pests. To control the other two pests, sweet potato whitefly and the western tarnished plant bug, growers use broad-spectrum insecticides and other types of insecticides known as insect growth regulators. Carrièère and his colleagues studied how Arizona farmers actually planted their crops and applied pesticides. The researchers compared the yield and pesticide use for 40 fields of non-Bt cotton, 21 fields of Bt cotton and 20 fields of Bt cotton that was also herbicide-resistant. In addition, each cotton field selected for the study was next to an uncultivated area. That allowed the researchers to compare ant and beetle biodiversity among the various cotton fields and the uncropped areas.
the cotton fields, the researchers used a type of statistical analysis called path analysis. Factors that affected biodiversity included the sandiness of the soil, use of broad-spectrum insecticides and insect growth regulators, number of cotton seeds planted per acre, and the amount and types of plants in the adjacent uncultivated areas. The researchers found that the type of cotton had no effect on how much insect biodiversity was in a particular field. “Yield, pesticides and effects on non-target organisms - we must look at those all together to assess the environmental impacts of transgenics,” Carrièère said. “The take-home message is that transgenic crops are very promising for reducing the impact of agriculture, but we need to study how they're integrated into the way we do agriculture.” (University of Arizona, 5/1/06, Agricultural Aviation, May/June 2006).
