Genetically modified corn hybrids with built-in resistance to the western corn rootworm, are on the horizon. Monsanto Corporation has submitted its registration materials to the U.S. Environmental Protection Agency and reportedly hopes for a limited commercial release for the 2001 growing season.

Dubbed the "billion-dollar pest" for its cost in insecticides and crop loss, is the western corn rootworm worried? Not likely. Can farmers relax? Not yet, according to Integrated Pest Management experts at the University of Illinois at Urbana-Champaign.

The western corn rootworm, it turns out, is a formidable opponent -- much more of a challenge than the corn rootworm beetle, which was the first pest tackled by a GM seed: Bt corn. The western corn rootworm probably showed up in the continental United States with the Mesoamerican wild ancestors of field corn. Very mobile, it has been called a man-made pest because of its expansion eastward with center-pivot irrigation systems. First identified in Kansas in 1868, flying adult western corn rootworm beetles advanced 50 miles per year, reached Illinois in 1964, and are now in East coast fields.

The western corn rootworm also has overcome nearly every weapon in the pest control arsenal, according to Michael E. Gray, an entomologist at the University of Illinois and Extension IPM coordinator. Here's a tally of the WCR's successes:

resistance to chlorinated hydrocarbon insecticides in the 1960s; resistance to methly-parathion (organophosphate) insecticides in Nebraska in the 1990s; resistance to carbaryl (carbamate) insecticides in Nebraska in the 1990s; and adaptation to crop rotation. "The latter is a very, very rare example of an insect adapting to and overcoming cultural practices," says Gray. Because western corn rootworms prefer to lay their eggs in corn, entomologists recommended rotation, since larvae could not survive on soybean roots. Chemical control in continuous corn was necessary, but rotation seemed to work.

Then in 1987 rotated seed corn fields in Ford County, Ill., showed significant western corn rootworm larval injury. By 1995, rootworms were inflicting serious economic damage in rotated fields in east-central Illinois and northern Indiana. Today, Gray estimates, growers across the northern Corn Belt are having to spend up to $15 per acre for in-furrow soil insecticides, even in rotated fields.

Grays says that when western corn rootworm-resistant hybrids hit the market, farmers will probably have to pay a $15-per-acre technology fee -- up to $400 million per year nationally -- for the transgenic seed. Will the seed displace insecticide costs and be a one-shot knockout of the billion-dollar pest?

"Transgenic hybrids will be one more tool," he says, "but farmers will be required to increase their management skills in order to prolong its utility." For example, because the western corn rootworm will feed on the GM plants' endotoxins twice during the growing season -- once as larvae on the roots and once as adults on foliage and pollen -- selection pressure for resistance will double. In contrast, corn borers feed on Bt corn only once per generation.

"Resistance to transgenic corn may develop in as little as five years or never be observed," says Gray. "If inheritance [of resistance] is dominant, then resistance is all but certain. If it is recessive, the technology may remain effective for many years." The key in maximizing the effectiveness of this new tool will be farmers' willingness to educate themselves, to forget comparisons to corn borers ("there are very important differences in the insects' biology and ecology"), and to use the new hybrids under an IPM umbrella, says Gray.

"Farmers will need to scout fields and trap beetles in midsummer the season before they intend to plant western corn rootworm-resistant corn," he says. "Current research indicates that only 50% of Illinois corn fields have economically significant populations of western corn rootworm. Knowing which 50% to plant will in effect leave a necessary refuge of 50% so that resistance can be avoided or slowed. But if farmers begin to use the GM hybrids the way they use soil insecticides -- on every acre as an insurance policy -- resistance is a foregone conclusion."

The issue of this next transgenic hybrid's impact on nontarget organisms is another important difference. The research that showed Bt corn's impact on the mortality of Monarch butterflies has heightened the EPA's focus on Monsanto's registration materials. In fact, Gray says, the EPA has invited north-central land grant university scientists to meet with agency experts in Indianapolis in the next few months. The group will address the issue of impact on nontarget organisms, including the closely related coleopterans such as lady beetles and beneficial ground beetles of the carabidae family.

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