Just as farmers begin a second year of sowing a biotech wonder--crops engineered to make their own pesticides--comes a new study showing that a type of moth can resist several of these toxins. The finding, published in today's issue of the Proceedings of the National Academy of Sciences, boosts fears that some insects could quickly develop resistance to these pesticides, bacterial proteins known as Bt toxins, and render them useless.
Bruce Tabashnik's team at the University of Hawaii and colleagues at the Biotechnology Research Institute in Montreal and at Clemson University in South Carolina studied one pest--the diamondback moth--that several years ago developed resistance to Bt in watercress fields sprayed with Bt toxins. By mating the Bt-tolerant strain with moths that succumb to the toxins, the researchers deduced that a single gene likely confers resistance to four different Bt toxins. What's more, a whopping 21% of a lab strain of nonresistant moths carry a copy of this gene, which Tabashnik's group has not yet identified.
The diamondback moth itself doesn't eat corn, cotton, or potato plants, the main Bt crops on the market. But some experts worry that pests targeted by the crops--bollworms and tobacco budworms, for example--could develop resistance. Companies selling Bt seeds hope to avoid that in part by designing plants that make more than one Bt toxin, but this strategy may not work if resistance to several toxins is tied to a single gene, says Tabashnik, who is now at the University of Arizona. Farmers are also trying to thwart resistance by growing plants that lack the Bt toxins near their fields, cultivating populations of normal insects that could swamp the resistance genes, says Randy Deaton, a Bt researcher at Monsanto, which developed some Bt crops.
Perhaps most alarming to some scientists is that 21% of the lab moths carried the resistance gene--a rate 10 times higher than that seen in any other bug. If the gene were that prevalent in the field, says entomologist Fred Gould of North Carolina State University, an entire pest population could become resistant in a year or two--an outcome that could hurt organic farmers, who rely on Bt sprays. Researchers had thought resistance was very rare. "The idea that frequency can be that high is a big deal," Gould says.
But there may be a silver lining: Once researchers have cloned the gene and studied the protein it codes for, Tabashnik says, they might be able to use that knowledge to make better Bt plants. Meanwhile, however, more Bt crops are going into the ground--giving pests time to develop resistance.