How is your genetically modified diet going? If you ate cereal, drank soda, munched baked snacks or used cooking oil this week, you very likely ate some engineered protein--now a staple of American fare.

During the past decade the amount of farmland devoted to genetically modified (GM) crops has increased more than 50-fold, to an estimated 222 million acres worldwide in 2005, according to the International Service for the Acquisition of Agri-Biotech Applications (ISAAA). The U.S. grows more than half this biotech harvest, followed by 20 additional countries. Today's top crops: soybeans, corn, cotton, and canola modified to tolerate specific herbicides or resist certain insects. Tomorrow new GM crops might withstand drought, resist viruses, grow bigger, yield pharmaceuticals and do other things nature never imagined.

But it is not all sunshine and sweet profit for GM farming. Controversy--and confusion--over the technology remains. "We havent had the asparagus that ate Cleveland," says geneticist Norman Ellstrand, director of the Biotechnology Impacts Center at the University of California, Riverside. "But there's been at least one notable event of engineered crop genes escaping from farms or field trials every year--and that doesnt give us comfort."

And GM crops suffer other growing pains. Their measurable benefit--in reduced pesticide use or increased yield--varies considerably, depending on the technology, crop and region. Moreover, preliminary research indicates that at least one kind of GM cotton is losing ground against pests. Finally, public debate over GM foods continues, pitting state and local legislatures--and sometimes entire countries--against each other. As Jane Rissler, deputy director of the food and environment program at the Union of Concerned Scientists, puts it: "From where I sit, genetically modified crops are not a slam dunk."

A Modified Farmscape
IT ALL BEGAN with business. Although relatively small compared with other agricultural product markets, the commercial seed market in the U.S. (about $5.7 billion) and worldwide (about $25 billion) is rapidly growing, particularly for major field crops, according to the U.S. Department of Agriculture. Fewer than half a dozen companies dominate the domestic seed market, and as biotechnology emerged, they saw an opportunity to genetically modify crop seeds with one or more desirable traits. Many farmers were willing to pay for premium seeds with these traits.

Today most GM crops contain genes enabling them to either resist insect pests or tolerate weed-killing herbicides [see box on page 44]. The herbicide-tolerant types contain genes enabling them to survive when exposed to broad-spectrum weed killers such as glyphosate (sold as Round-up), potentially allowing farmers to forgo more toxic chemicals that target specific weed species. The insect-resistant varieties of GM crops make their own insecticide, a property meant to reduce the need for chemical sprays. To date, insect resistance has been provided by a gene from the soil bacterium Bacillus thuringiensis (Bt). This gene directs cells to manufacture a crystalline protein that is toxic to certain insects--especially caterpillars and beetles that gnaw on crops--but does not harm other organisms.

In 2005 herbicide-tolerant varieties represented 87 percent of the U.S. soybean crop and 61 percent of the cotton crop. That same year Bt varieties represented 35 percent of the U.S. corn crop.

"These crops have shown clear benefit," says Zigfridas Vaituzis, a senior scientist at the Environmental Protection Agency. "With herbicide-tolerant crops, farmers can spray their fields with relatively safe, biodegradable chemicals," Vaituzis says. "For its part, Bt cotton has cut pesticide use on cotton crops by half. A conventional cotton crop may take 12 applications of various pesticides each season. Halving that means less exposure to those chemicals, both on the farm, in groundwater and in spray drift in the surrounding community. Those are measurable benefits."

Early environmental fears about potential negative effects of Bt corn pollen on monarch butterflies, or of Bt toxins on soil organisms, have not materialized in repeated studies. "We've seen no uptake of Bt toxins by other plants or any effect on soil microbes," says Guenther Stotzky, a soil microbiologist at New York University. "That's why Im no longer a critic of Bt crops."

A Risky Escape
BUT AT LEAST one environmental risk looms: escape. Researchers have long worried that unwitting insects or the right wind could carry GM crop pollen to weedy plant relatives, fertilizing them. The newly endowed plants could then break ecological rank, becoming "superweeds" that push out native plants or resist pesticides.

Until recently, that fear remained fiction, as scientists engineered farm crops that mostly lack wild, weedy relatives in the U.S. But in August 2006 ecologists at the EPA reported the first wild outbreak of a GM crop: a turfgrass.

In central Oregon the Scotts Miracle-Gro Company had field-tested an herbicide-tolerant variety of creeping bentgrass, for possible use on golf courses. Surveying the nearby area, EPA scientists found wild grass with the genetic modification at six sites, some more than two miles away from the test plots.

Reporting in the journal Molecular Ecology, the scientists suggested that wind carried the modified grass's seeds and pollen to the locations where new plants emerged. The USDA has launched an environmental impact assessment of the transgenic grass to determine whether it could spread and become invasive.

The runaway grass alarms scientists, in part because they worry that next-generation GM crops--such as "biopharms," or plants engineered to yield pharmaceuticals--could similarly escape. "When we start growing antigens that could get back into the food chain, this kind of event becomes much more serious," Stotzky says.

Already the USDA has come under fire for its oversight of biopharming. Four environmental groups have successfully sued the agency over biopharm field trials in Hawaii, in which corn and sugar cane plants were modified to make human hormones and vaccine ingredients to fight HIV and hepatitis B. In August a U.S. District Court judge in Hawaii ruled that the USDA broke national environmental laws by allowing the open-air field trials without first considering their environmental impact, particularly on endangered species. In response, the USDA has overhauled its permit process.

Beyond the field, experimental GM crops have repeatedly found their way into the food supply--twice during the summer of 2006 alone. First, Riceland Foods, the country's largest marketer of rice, discovered trace amounts of an unapproved herbicide-tolerant rice strain in its commercial rice supplies, which are grown across a wide region of the southern U.S. In response, the European Union placed strict testing requirements on U.S. imports, sending U.S. rice prices tumbling and provoking a class-action lawsuit by farmers alleging that Bayer CropScience--which had bred the rice--was negligent in preventing GM seeds from contaminating the nation's seed supply.

Also last summer, the environmental groups Greenpeace and Friends of the Earth reported that their tests of processed rice foods in London had turned up five samples of rice products imported from China, such as vermicelli and rice sticks, containing an unapproved insect-resistant rice variety. The European Commission urged member states to step up controls of GM foods, which are not approved for consumption in Europe.

But that will be difficult to do, Ellstrand says. In an ongoing 1.5-million study funded by the National Science Foundation, he leads a team of biologists and social scientists collaborating to analyze the unintended spread of engineered plant genes. One serious problem is the frequent disconnect between policymakers, seed salespeople, regulators and farmers about how to grow and control GM crops," Ellstrand explains. As seeds and food cross borders, he adds, that coordination dissolves further.

A Long Lens
WHEN IT COMES TO basic biology, even GM crop proponents worry that gains made by modified plants are only temporary. After all, evolution does not stop for technology. Insects, for instance, may evolve strategies for overcoming Bt technology and eventually consume the transgenic plants with no effect.

Or nature may take a different tack, as suggested by the first long-term economic impact study of Bt cotton in China. That study, presented by Cornell University researchers at the July 2006 meeting of the American Agricultural Economics Association, found that farmers planting Bt cotton--designed to defy the leaf-eating bollworm--initially prospered, cutting pesticide use by 70 percent. By year seven of Bt cotton farming, however, secondary insects such as mirids crept in, replacing the bollworm as the star scourge--and forcing farmers to return to typical spraying levels, even as they paid for Bt seed, which costs two to three times more than conventional seed.

That does not surprise Alison G. Power, an ecology professor at Cornell. "When we breed traditional plants that are resistant to some particular pest, the next most important pest moves in," Power explains. "We see this all the time with plant viruses."

Rebecca Goldburg, a senior scientist at Environmental Defense, predicts that farmers will eventually lose Bt as an effective control against insects and will then move on to another chemical control. "Many of us view this current generation of biotech crops as a kind of diversion, rather than a substantive gain, for agriculture," Goldburg says.

Like scientists, politicians are at odds over GM crops. During the 2005 legislative session, 117 pieces of legislation related to agricultural biotechnology were introduced in 33 states and in the District of Columbia. Many state legislatures attempted to disallow local and county efforts to ban or limit GM seeds and crops. Of the 23 state bills that passed during 2005, two thirds supported GM technology, according to the Pew Initiative on Food and Biotechnology.

More than anything, the public is just plain confused about GM crops, as reported in a survey released in 2005 by the Food Policy Institute at Rutgers University. In the survey of 1,200 U.S. residents, about half said they were unsure or could not take a position on GM foods. Roughly a fourth of them approved of GM technology, but almost as many disapproved. Lead author William Hallman, a Rutgers psychologist, concluded that people "seem to be willing to believe just about anything they hear about GM foods." The study suggests that fewer than half of Americans realize that supermarkets regularly sell GM foods.

Like them or not, GM crops are poised to grow--and not just in the U.S. In 2005, according to the ISAAA, 38 percent of the land planted in GM crops was in developing countries, which desperately need plant varieties that tolerate drought and improve yield, among other traits. In 2006 Iran produced its first full-scale commercial seed supply of Bt rice. China is expected to follow. "Yes, this technology will have to be modified, due to resistance factors, the appearance of new pests and other challenges," Vaituzis says. "But genetically modified crops are here to stay."

KATHRYN BROWN is a science writer based in Alexandria, Va. She frequently writes about botany, ecology and earth science for magazines such as Scientific American and Science. Brown is a member of the board of the D.C. Science Writers Association.