Are super bugs resisting super hybrid crops?

Pesticide use is surging among U.S. corn farmers who are worried some insects have become resistant to genetically modified versions of the crop.

That’s an unexpected reversal since one of the promises of engineered corn when it was introduced 17 years ago was its ability to kill pests. The use of soil insecticides for the crop plunged 90 percent through 2010, according to the U.S. Department of Agriculture.

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. 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. (NYSE:MON) 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.

That view is driving up profit for pesticide makers like FMC Corp. (NYSE:FMC) and American Vanguard Corp. (NYSE:AVD). They’re marketing corn insecticides as a kind of insurance policy that costs $12 to $25 an acre. Root-eating larvae of the flying insect has historically cost U.S. farmers $1 billion in expenses and lost harvest, according to USDA estimates.

Pesticides unnecessary

Some scientists are skeptical that a return to pesticide use is in the long-term interests of farmers. Soil insecticides don’t improve root health or yields when the corn is already producing its own insecticide, according to a paper by University of Illinois scientists published online April 25 by the Journal of Applied Entomology. Iowa State University researchers reached a similar conclusion last year.

Chemical insecticides are simply redundant, said Michael Gray, a University of Illinois entomologist.

“It’s pretty clear where the science and the scientific community is on this point,” Gray said. “It really does not add much.”

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.

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