by DAN CHARLES
Hidden in the soil of Illinois and Iowa, a new generation of insect larvae appears to be munching happily on the roots of genetically engineered corn, according to scientists. It’s bad news for corn farmers, who paid extra money for this line of corn, counting on the power of its inserted genes to kill those pests. It’s also bad news for the biotech company Monsanto, which inserted the larvae-killing gene in the first place.
In fact, the gene’s apparent failure, as reported in the journal PLoS One, may be the most serious threat to a genetically modified crop in the U.S. since farmers first started growing them 15 years ago. The economic impact could be “huge,” says the University of Arizona’s Bruce Tabashnik, one of the country’s top experts on the adaptation of insects to genetically engineered crops. Billions of dollars are at stake.
The story of how this happened is long and complicated, but the details are important, so let’s start at the beginning.
Almost the entire agricultural biotech industry has been built on just two genetic traits, and our story involves one of them.
The gene (actually a family of genes) in this story — the first pillar of the industry — was copied from an insect-killing bacterium called Bacillus thuringiensis, or Bt. In the 1980s, scientists managed to insert a Bt gene into plants, and voila, the plant cells started manufacturing the same worm-killing toxin as the bacteria. (The other big gene for the agricultural biotech industry allows a plant to survive doses of the popular herbicide glyphosate, widely known by Monsanto’s trade name, Roundup.)
So-called Bt corn went on sale in the late 1990s. It has been astonishingly effective against the European corn borer, a common pest.
But from the beginning, scientists worried that biotech companies were overusing Bt and increasing the chances that it would eventually stop working. Why? The key word is resistance.
The more widely you spray any insecticide, the more likely you are to uncover and promote the growth of a new strain of insects that’s resistant to your insect killer. It has happened with one insecticide after another over the decades. Eventually, scientists said, the same thing would happen to a crop that carries its own insecticide. Covering fields with Bt crops would lead to a strain of insects that the crops didn’t kill.
So university researchers and federal regulators came up with a strategy to preserve Bt’s effectiveness. First of all, they said Bt crops (mainly corn and cotton) should be extremely effective. Ideally, they would kill 99.99 percent of all the target insects that fed on them.
And for those rare insects that survived, regulators came up with a second line of defense, to prevent resistant insects from mating and producing lots of resistant offspring. Farmers who grew Bt corn (or cotton) were required to grow non-Bt crops on some of their farm, as a “refuge” for normal insects. That way, the rare, surviving, resistant insects would probably find non-resistant mates, instead of each other, and their offspring still would (likely) be killed by the Bt corn.
To the surprise of some environmentalists, the strategy has worked. There’s no evidence that the European corn borer has evolved resistance to the Bt toxin. The same goes for some insects that feed on cotton, such as the pink bollworm — at least in the United States.