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Bt Corn Technology Full of Possibility, Perplexity

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Written Friday, November 22, 1996  

Bt corn, which is genetically engineered to be insect-resistant, appears to be doing its job. But the long-term prognosis for Bt-enriched crops is still up in the air, experts say.

Bt corn uses the natural insecticide produced by the bacterium Bacillus thuringiensis (Bt). By putting the Bt gene in corn, scientists have given corn plants their own defense against European corn borer.

Scientists can't yet count the number of studies necessary to fully assess Bt. But they have no doubt that the effort will take years. In the meantime, farmers can look forward to the first substantial data on Bt corn yield later this year.

Besides studying yield competitiveness, researchers are looking at the long-term prospects for Bt corn. Among questions to be answered: Which part of the plant should express the Bt trait; does Bt work better at certain times during plant development; and, would the overuse of Bt allow insects to become Bt resistant some day?

Experts say that problems sometimes occur when technology is overused, just as over-prescribing antibiotics to people can result in treatment-resistant bacteria. If farmers begin to plant Bt corn more than any other, scientists wonder if insects could develop resistance.

"Problems with pests resistant to Bt crops are possible," says Purdue entomologist Larry Bledsoe. "While the Bt-corn concept appears to be a very effective barrier against European corn borer, it may exert a strong force for insect adaptation. But resistance management and the fact that corn borers can feed on numerous plants besides corn will probably slow, or possibly prevent, development of resistance."

Bledsoe also says that if resistance to Bt were to occur, the worst result would be a return to control methods being used today.

Marshall Martin, professor of agricultural economics and director of Purdue's Center for Agricultural Policy and Technology Assessment, says Bt offers distinct advantages. "It's often found in organic gardening products," he says. "It is much safer for people than insecticides. It has been approved by the EPA, the FDA and the USDA, which found no negative human health aspect."

The natural insecticide not only eliminates the need for other insecticides, it's safe for animals and beneficial insects, and it degrades in sunlight. Also, because the gene works by producing a protein that is easily digested by people and animals -- but not by some insects -- there is no concern about it being placed in food.

Martin agrees that the potential for problems is there, but doubts that corn farmers will see extreme problems. "The last thing a seed company wants is for seed not to work after they've put all of the R-and-D time and effort into it," he says. "The farmer doesn't want the seed to fail because that would deny him another tool, and it's one that he needs. The environmentalists don't want the seed to fail because then farmers will go back to spraying insecticide."

Martin says farmers will agree that limited control makes sense. "You can live with a yield loss of 3 to 4 bushels per acre, but not 10 to 15," he says. "So we don't need to kill every insect out there, just suppress them."

Martin says farmers will embrace Bt crops also because they can be more strategic against insect attacks: "It's a corn borer. It bores inside the plant, and once it's there you can't do anything about it." Bt crops, whose insecticidal trait is in plant tissue can control pests that might otherwise go unnoticed until they cause lodging.

"If you ride in the cab of a combine, as I have done, and you see these stalks hit the corn head and fall over where the grain can't be harvested, it just hits the farmer right in the pocketbook," Martin says. "That's money that's falling on the ground."

Farmers whose fields are infested can lose 10 percent to 15 percent or more of their crop. "At corn prices that we're seeing right now, there's good incentive to try to control it," he says.

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