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Smarter than a rootworm? Don't count on it

Agriculture.com Staff 01/30/2007 @ 12:15pm

So, you think you're smarter than a corn rootworm? Well, just consider what the little buggers are doing to survive and even outsmart our brightest scientists.

For years, we managed corn rootworms with a corn-soybean crop rotation. Any rootworm eggs laid in a corn field one year hatched and died in a bean field the next summer, for lack of any corn roots to munch on.

But a few years ago, a few rootworms in Illinois got smart and began skipping a year before hatching, when the field was back in corn. This extended diapause, or dormancy, is spreading and is now seen to some degree in Iowa and other Corn Belt states, says Iowa State University entomologist Marlin Rice.

Some rootworms have gotten smarter yet, and learned to lay eggs in soybean fields. Rice has found corn rootworm beetles in fields that have been in continuous soybeans for several years. "Not heavy populations," he says, "but growing."

Fortunately, the new method for controlling rootworms -- biotech seed with built in traits such as Herculex and YieldGard insect control -- has come along at this time. Unfortunately, these worms don't give up easily. A few outsmart even the super scientists, and the biotech seed fails.

One theory on this, says Rice, is that the Bt poison is expressed at different concentrations in different parts of the root tissue. Maybe, he says, some rootworms sort of "graze" on the roots, taking a little bite here and there until they find a spot they really like. If it's a spot with a lower concentration of Bt, the rootworm lives. And, of course, that smart one reproduces.

Don't worry, there will be new rootworm products and techniques come along. But worry a little, because they'll fail, too.

So, you think you're smarter than a corn rootworm? Well, just consider what the little buggers are doing to survive and even outsmart our brightest scientists.

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