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by Mary Losure
May 16, 2000
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The debate over biotechnology seems to get louder with each passing month. Critics of bioengineered crops say they're a threat to consumers and the environment. Most scientists dismiss fears about the health risks of genetically-altered crops. But there is no scientific consensus when it comes to their environmental impact.
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ON A GRAY early spring day, protesters rallied outside the international agribusiness Cargill in Minnetonka. Some in the crowd wore biohazard suits and held signs with slogans like "Biotechnology, the Seed of All Evil." Inside Cargill's corporate headquarters, spokesperson Robbin Johnson took a very different stance. "The products are safe that have been introduced into the marketplace, they are environmentally friendly, so there is no need to concerned about their effects on either human health or the environment," Johnson said.
Most scientists would agree there is little reason to worry about the health risks of genetically-modified crops. The National Institutes of Health say the newly developed crops pose no more risks to consumers than traditional varieties. But the evidence on the environment is less clear.
A number of scientists are investigating a middle ground between the doomsday fears raised by activists, and the blanket assurances offered by agribusiness companies.
In his laboratory at the University of Minnesota, entomologist David Andow raises an insect pest known as the European corn borer. The insects cost American corn farmers millions of dollars every year.
So Monsanto and other agribusiness companies developed corn genetically engineered to kill corn borers. They transferred a gene from naturally toxic bacteria known as Bt into corn plants. The result: corn plants which make their own insecticide.
But Andow and other entomologists say its only a matter of time until corn borers develop resistance to Bt corn, in the same way bacteria become resistant to antibiotics. "The issue is not a question of if insects will become resistant to the crops, but when they will become resistant to the crops," he says.
"This is what we entomologists call a pesticide treadmill, so you're evolving resistance and having to replace them constantly. So you're constantly turning over your pest-control methods."
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"So when I was out in corn fields during the pollen-shed period, and I found that milkweeds were getting dusted with corn pollen, I wondered what would happen if that corn pollen had come from a Bt corn field," he said.
Losey went back to the laboratory. He dusted some milkweed leaves with pollen from traditional corn and other milkweed leaves with pollen from Bt corn. Then he fed them to the monarch caterpillars. The ones that ate the leaves dusted with traditional corn pollen all survived. Of the ones that ate the leaves dusted with Bt corn pollen , nearly half died.
Such laboratory results can't determine how monarch butterflies in the wild are being affected, but Losey says scientists urgently need to find that out.
"We grow 80 million acres of corn in the U.S.," he says. "Over a quarter of that is planted to Bt corn. We know that milkweed, a big part of the population of milkweed, which is the only host of monarch butterflies, occurs around corn fields."
Another little-understood issue is what effect bioengineered crops may have on wild plants. Scientists have known for years that cultivated crops can interbreed with wild relatives. For example, cultivated sunflowers can interbreed with wild sunflowers. When that happens, genes from the crop pass into the wild population.
Bioengineered crops contain genes from bacteria, insects, animals, fish, and other organisms, what scientists call transgenes. These transgenes can also move from crops into wild plants.
Alison Snow, a plant ecologist at Ohio State University, has studied the flow of conventional genes from crops to wild relatives for years. She says the flow of transgenes to wild plants is only just beginning. "In the U.S., it's not going to happen with corn or soybeans, because they don't have weedy relatives. In the U.S. it will be crops that aren't really commercialized yet with transgenes."
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Snow expects transgenes from canola, squash and rice to move into wild populations. The process will accelerate as genetically-engineered forms of those crops become more widely grown. But the first evidence of transgenes moving from cultivated plants to weeds has already surfaced.
Tony Hueber, a grain farmer in Alberta, planted canola in 1997 with a transgene that makes the canola resistant to herbicide; meaning the plants can be sprayed with herbicides like Roundup and survive. The next year, he noticed something odd about a patch of weeds in another field.
"How I came to find out that it was genetically altered was that it did not die when it was sprayed with Roundup," he says.
The weeds didn't die because a transgene for herbicide resistance had jumped from the crop to the wild. "That happened through cross pollination the previous year. That was something that I was told we could expect would not happen."
By the next year, Hueber had weeds in his fields that were resistant to three different herbicides.
DNA and chemical testing by the Alberta Department of Agriculture showed the genes for all three types of resistance had flowed into the weeds from herbicide resistant varieties of canola.
But plant ecologist Snow does not think such problems are reason to condemn all genetically engineered plants. Snow says the technology has great promise in some situations.
"Like in Hawaii, the papaya industry was failing," Snow says. "And when transgenic disease resistant payayas were introduced, the farmers were really happy about that, there were some benefits that seemed to outweigh the risks, no risks were identified with that particular crop."
Since 1992, the U.S. Department of Agriculture has approved dozens of applications for genetically-modified crops without extensive testing to determine their environmental safety.
But the discovery by Cornell's John Losey that bt pollen was toxic to monarch butterflies galvanized public awareness about possible environmental dangers from genetically-modified crops.
That study and other research may cause regulators to scrutinize future products more closely.
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