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Genetically Modified Corn Helps Common Kind, Too

An ear of genetically modified BT-corn waits to be harvested on the farm of Gary Shedd, near Rockton, Ill., in 2003. (Getty Images)

Fifty years of records from cornfields in five Midwestern states show that genetically modified corn has dramatically reduced populations of a common corn-eating worm, the European corn borer. That has put more money in farmers' pockets, but paradoxically most of the financial benefit went to farmers who did not grow those new kinds of corn.

Why? The fields of conventional corn also had the benefit of fewer worms because the fields of genetically engineered corn nearby had killed off the insects. But the conventional corn was cheaper to grow because the seed costs less. It's similar to the situation of people who decide not to get a flu shot -- if everyone around them gets the shot, they're still less likely to get the flu. They get the benefit without the pain.

The European corn borer hitched a ride to the New World on a ship from Europe in 1917. It loves corn and quickly spread across corn-growing areas of the Midwest. Every year scientists from the U.S. Department of Agriculture went into cornfields and counted those worms. The new study, published in the journal Science, is based on those records.

  • The United States grows about 88 million acres — more farmland than any other crop
  • The largest share of the corn harvest becomes chicken, hog, and cattle feed. About 30 percent goes into making ethanol.
  • Genetically engineered corn was first sold in 1996, and since then, scientists have introduced a variety of new genes.  They include genes that allow the plant to withstand popular weed killers, as well as Bt genes that produce toxins that kill the European corn borer and another pest, the corn root worm.
  • Farmers who grow Bt corn are required to plant at least 10 percent of their fields with conventional corn. This "refuge" is intended to delay or prevent the emergence of insects that are resistant to the effects of Bt corn.

    Here's how: In the vast population of corn borers, a few individual insects may possess a genetic mutation that gives them resistance to Bt. If 100 percent of the corn crop is toxic to corn borers, it is more likely that so many susceptible insects will be killed off that the rare, resistant corn borers will find each other and mate, creating many offspring that carry this resistance. If this happens, the population of resistant insects will explode. The hope is that the refuges of non-Bt corn will sustain a population of insects that remain susceptible to Bt.

A Pattern Of Infestation

"Amazingly, these data sets were just sitting in filing cabinets," says William Hutchinson, a specialist on insects at the University of Minnesota.

Hutchinson and a group of colleagues pulled out those files and took a closer look. For most of the past 50 years, he says, there was a regular pattern to the corn borer infestation. "About every six to seven years there would be an outbreak, and then they would naturally decline."

But starting 14 years ago, corn borer populations started falling and the occasional big outbreaks stopped. Hutchinson says there's a simple reason: Also 14 years ago, farmers started growing corn that contained a gene inserted in the laboratory. This genetically engineered corn is poison to corn borers, so when the insect larvae start feeding, they die.

The gene came from a kind of bacteria called Bacillus thuringiensis, or Bt, so the corn is known as Bt corn. It has become extremely popular among farmers.

"We're up to about 63 percent of the total U.S. [corn] acres," Hutchinson says. "Fifty-five million out of 88 million acres are now Bt corn."

Hutchinson and his colleagues estimate that farmers made $7 billion in extra profits over the past 14 years because fewer worms were eating their corn. And two-thirds of that added profit came from fields of conventional corn.

Advantages Of Conventional Corn

Hutchinson and his colleagues are highlighting the financial rewards of growing conventional corn for their own reasons and they want farmers to keep planting it. If farmers plant only genetically engineered corn, it increases the risk that a new kind of corn borer will emerge -- one that is resistant to the effects of Bt.

Bruce Tabashnik, an entomologist at the University of Arizona, says it's not just a theoretical danger. "There are some other situations where insects have evolved resistance to Bt crops, including Bt corn," he says. For instance, in Puerto Rico, farmers once grew Bt corn almost exclusively, and insects called fall armyworms used to die when they ate it. Now, they don't.

To help keep the same thing from happening here, farmers in the U.S. are supposed to plant conventional corn on at least 10 percent of their acres. These are so-called "refuges" where corn borers can live in peace. But some farmers don't do it.

Tabashnik, who was not involved in the new study, says this research could help convince more farmers that it's not just a good idea to plant conventional corn -- it's also profitable.

"It's a wonderful result," he says. "This example is sort of the poster child for a case where resistance has not evolved. We can see what wonderful benefits there are, and hopefully some of the lessons from this case can be exported and encourage growers more generally, globally, to adopt the refuge strategy."

Some farmers, in fact, seem already to have figured out that conventional corn can be more profitable. There are reports that demand for Bt corn has leveled off.

But even when farmers want to move away from Bt corn, it's not always easy for them to do it. Seed companies such as Monsanto and DuPont now sell seeds that contain lots of different traits. Sometimes, if farmers want one of those genes -- one that kills the corn rootworm, for instance -- they also get others that they may not want, such as the Bt gene that kills the European corn borer.

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MARY LOUISE KELLY, host:

According to a report in today's issue of the journal Science, genetically modified corn has dramatically reduced populations of a common corn-eating worm. That's put more money into farmers' pockets, but paradoxically, most of the financial benefit went to farmers who did not grow those new kinds of corn.

NPR's Dan Charles reports.

DAN CHARLES: The insect is called the European corn borer. This little worm, which also turns into a moth for part of its life, hitched a ride to the New World on a ship from Europe in 1917. It loves corn and quickly spread across corn-growing areas of the Midwest.

Every year, scientists from the U.S. Department of Agriculture went into corn fields and counted those worms.

Professor WILLIAM HUTCHISON (Head, Department of Entomology, University of Minnesota): And amazingly, these data sets were basically just sitting in filing cabinets.

CHARLES: William Hutchison is an insect specialist at the University of Minnesota. He and a group of colleagues pulled out those files and took a closer look. For most of the past 50 years, he says, there was a regular pattern to the corn borer infestation.

Prof. HUTCHISON: About every six to seven years there would be an outbreak, and then they would naturally decline.

CHARLES: But starting 14 years ago, corn borer populations started falling, and the occasional big outbreaks stopped. Hutchison says there's a simple reason. Also 14 years ago, farmers started growing corn that contains a new gene inserted in the laboratory. This genetically engineered corn is poison to corn borers. So when they start feeding, they die. The gene came from a kind of bacteria called Bacillus thuringiensis or Bt. So the corn is known as Bt corn, and it's extremely popular.

Prof. HUTCHISON: We're up to about 63 percent of the total U.S. acres, so about 55 million out of 88 million acres are now Bt corn.

CHARLES: Hutchison and his colleagues estimate farmers made $7 billion in extra profits over the past 14 years because fewer worms were eating their corn. What's more surprising? The biggest boost in profits was from the fields of conventional corn. Those fields also had fewer worms because all the Bt corn planted nearby had killed them off. But farmers growing traditional corn didn't have to pay for the Bt corn seed, which is more expensive.

Prof. HUTCHISON: The non-Bt acres are actually receiving about two-thirds of the total $7 billion benefit.

CHARLES: It's a little like if everyone around you gets a flu shot, they're less likely to infect you with the flu. You get the benefit without the pain.

Now, there's a reason why Hutchison and some of his colleagues are highlighting the money farmers can earn by planting conventional corn. They want farmers to keep planting it. Because if farmers planted only genetically engineered corn, you'd be more likely to see a new kind of corn borer emerge - one that's resistant to the effects of Bt.

Bruce Tabashnik at the University of Arizona says it's not just a theoretical danger.

Professor BRUCE TABASHNIK (Head, Department of Entomology, University of Arizona): There are some other situations where insects have evolved resistance to Bt crops, including Bt corn.

CHARLES: For instance, in Puerto Rico, farmers once planted almost a hundred percent Bt corn, and insects called fall armyworms used to die when they ate it. Now, they don't. To help keep the same thing from happening here, farmers in the U.S. already are supposed to plant conventional corn on at least 10 percent of their acres. These are so-called refuges where corn borers can live in peace. But some farmers don't do it.

Tabashnik, who was not involved in the study released today, says this research could help persuade more farmers that it's not just a good idea to plant conventional corn; it's profitable.

Prof. TABASHNIK: It's a wonderful result. This example is kind of the poster child for a case where resistance has not evolved. And hopefully, some of the lessons learned from this case can be exported and encourage growers more generally, globally to adopt the refuge strategy.

CHARLES: Some farmers, in fact, seem to figure this out on their own. There are reports that demand for Bt corn has now leveled off. But even when farmers want to move away from Bt corn, it's not always easy for them to do it.

Seed companies - the big ones are Monsanto and DuPont - now sell seeds that contain lots of different traits. Sometimes, if farmers want one of those genes - one that kills the corn rootworm, for instance - they also get the ones they may not want, such as the Bt gene that kills the European corn borer.

Dan Charles, NPR News, Washington

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