Is GM corn leading to overuse of insecticides as pests develop resistance?

Jack Kaskey | Bloomberg | June 12, 2014

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Whether the return to pesticide use makes sense, or is simply spurred by a chemical industry marketing campaign, is at the center of one of the biggest debates in the corn belt this spring. Pesticide use is surging among U.S. corn farmers who are worried that some insects have become resistant to genetically modified versions of the crop. At the heart of the controversy is whether snuffing out pests in the short term with chemicals may create a worse problem down the road.

Farmers say they need to do whatever it takes now to control the western corn rootworm, the most damaging U.S. corn pest. Although Monsanto Co. designed its corn to kill the worms, resistant bugs have been found in four states and growers say pesticides are needed again to protect their crops. It would be “financial suicide” to plant rootworm-killing corn without a soil insecticide as a secondary way to control the larvae, said Illinois farmer Mike Jenks, echoing the views of growers across the Midwest.

Some scientists are skeptical that a return to pesticide use is in the long-term interests of farmers. An EPA panel of scientific advisers warned in March that “the use of a soil insecticide with a Bt hybrid should not be done.” That echoes a 2012 warning to the EPA from 22 corn entomologists that “an insurance-based approach” to insecticides “will only increase insect resistance.” Entomologists also warn that the additional insecticide may exacerbate the resistance problem that farmers fear. That’s because pairing pesticides with engineered corn exposes insects to extra toxins, delaying maturity. That leads to increased mating between resistant worms, hastening the evolution of rootworms that aren’t vulnerable to GMO corn.