June 15, 2012 | 9
Cotton genetically engineered to produce a natural pest killer not only reduces the spraying of pesticides, but has also boosted the populations of beneficial insects, according to a new study. The study monitored the impacts of so-called Bt cotton over more than 20 years and 2.6 million hectares of farmland in northern China and found that transgenic pest control produced knock-on benefits for surrounding fields of different crops—a benefit for the more than 10 million small-scale farmers in the region who grow these crops.
Bt is a toxin derived from the bacterium Bacillus thuringiensis, which is lethal to the cotton bollworm (the primary pest in Chinese fields and a moth larvae) but harmless to other insects and animals, including people. To assess the impacts of this natural pesticide genetically engineered into cotton, scientists monitored 36 sites in six provinces of northern China from 1990 to 2011. They found that Bt cotton fields endured less organophosphate or pyrethroid insecticide spraying and thus boasted higher populations of ladybugs, lacewings and spiders—insect predators.
As a result, Bt cotton fields had fewer aphids—an insect pest not poisoned by Bt but nevertheless controlled thanks to the boosted populations of predators. That effect also spread to adjacent fields of maize, peanuts and soybeans. “The deployment of Bt crops may favor biocontrol services and enhance economic benefits not only in Bt crop fields but also in the whole agricultural landscape,” the scientists wrote in a letter presenting the research published in Nature on June 14. (Scientific American is part of Nature Publishing Group.) Crops engineered to produce the Bt toxin now cover some 66 million hectares of farmland globally.
In the U.S., similar research has found that Bt cotton not only reduces insecticide use, but also decreased the overall biodiversity in a given field. In addition, the protein crystal that makes Bt deadly—Cry1Ab—has been found floating in streams fed by runoff from agricultural fields. And, unfortunately, American pests like the western corn rootworm have been developing the ability to tolerate Bt, suggesting that resistance to the insecticide may become common unless measures are taken, such as planting non-Bt crops in adjacent fields.
Development of such resistance might prove a particular blow to farmers in China and the rest of the developing world as few alternatives to Bt exist to control the pests that plague their fields. In fact, a plague of bollworms in the early 1990s paved the way for the speedy government approval of the cotton genetically modified to produce the Bt toxin to cut down on the bollworms, insecticide pollution and farmer costs. Learning how to interweave natural control via predators such as ladybugs with the benefits of crops protecting themselves with the Bt toxin may be a key step on the road to a more sustainable agriculture.