It's food for thought

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Seventy percent of the food American consumers eat has a genetically engineered ingredient in it, mostly from modified corn and soybean crops, says Galen Dively, professor of entomology at the University of Maryland in College Park.

In the mid-1990s, the agriculture industry commercially introduced four crops to farmers -- corn, soybeans, cotton and canola -- that, through gene splicing, have become herbicide-tolerant and resistant to the crops' main predator pests.

"It's very easy for [farmers] to use because it comes in a seed. It increases yield, and it's not that expensive," says Mr. Dively, extension specialist for pest management for the Maryland Extension Service in College Park. He holds a doctorate in entomology.

Farmers responded enthusiastically to the new crop varieties, even though the seeds cost more, and rapidly and widely adopted herbicide-tolerant (HT) soybeans and cotton, followed by insect-resistant (Bt) cotton and corn, according to the Economic Research Service (ERS), an in-house research agency of the U.S. Department of Agriculture (USDA).

"It's safer because we're not using a bunch of synthetic pesticides. We're reducing that," says Douglas Tregoning, county extension director of the Montgomery County Cooperative Extension in Derwood.

In 2005, 87 percent of the acres farmers planted with soybeans contained the HT strain, as did 61 percent of the cotton acreage and 26 percent of the corn acreage, as stated in USDA survey data, published on the agency's Web site (www.ers.usda.gov).

The HT strain is resistant to specific herbicides that, if applied at the wrong time of the growing season, can kill the crop along with the targeted weeds. With HT crops, herbicides can be applied once the crops are growing instead of before or when the crops are planted. The most common HT crop is called Roundup Ready and is resistant to glyphosate, which is used on grasses, sedges and broadleaf weeds.

Crops modified to be insect-resistant contain a gene that produces a protein toxic to certain insects. The genes for Bt cotton and corn come from the soil bacterium Bt, or Bacillus thuringiensis, and are spliced into the crops to protect the plants from predators. The bacterium produces more than 60 different kinds of proteins.

"The corn is producing its own insecticide internally," Mr. Dively says, adding that for more than 50 years, Bt, which is benign to animals and humans, has been used in insecticides. "This Bt protein is expressed in the plant at a very high dose," he says.

Bt cotton protects against the tobacco budworm, the bollworm and the pink bollworm caterpillars. Bt corn protects against the European corn borer, which likes to eat the cornstalk, and the corn rootworm.