EPA OKs Gene-Altered Bt Corn
But questions remain about impact on butterflies
THURSDAY, Oct. 18, 2001 (HealthDayNews) -- Does Bt corn pollen kill monarch butterflies, or doesn't it?
The government is siding with those who say it's safe. This week the Environmental Protection Agency (EPA) told the biotech industry that it can continue producing corn that's genetically engineered to poison its major insect pest. The agency's approval is for the next seven years, the period for which registrations are renewed.
But there are still those who say Bt corn could be dangerous to the environment. "We still don't have the data to come to the conclusion that the risks are negligible," says University of Minnesota ecologist Karen Oberhauser, a research associate in the department of ecology, evolution and behavior.
In the last few years, the controversy has shaken up the corn-growing industry and fueled opposition to all genetically engineered crops. But the latest research, which bolsters the EPA's position, finds little evidence that the most commonly used types of genetically engineered corn harms the larvae of the large orange-and-black butterflies.
Galen P. Dively, a University of Maryland entomologist, and five other scientists in the United States and Canada began their study two years ago after another study showed that pollen from one type of Bt corn could be toxic to monarch larvae.
Dively, after feeding the suspect pollen to monarch larvae in the field and in the laboratory, says the impact on the butterfly is negligible. "I think we have pretty solid evidence that the two major types of Bt corn that most farmers grow are nearly harmless to monarchs," he says. His findings were published last month in the Proceedings of the National Academy of Sciences.
Farmers are supposed to plant ordinary corn near fields of altered corn so that insects known as European corn borers will feed at least partly on that corn and not become resistant to the altered corn's toxin.
Dively's study is based on the monarchs' habit of eating milkweed plants, which often grow beside cornfields and are covered by pollen from the Bt crops. Before Dively and his team could see any effect at all, the butterfly larvae had to eat more than 1,000 grains of pollen per square centimeter of milkweed. The average amount of corn pollen blown on to the milkweed is 150-200 grains per square centimeter -- unless the weather is very dry, when the amount can climb to 600 grains per square centimeter. Dively says that's still nowhere near the danger point.
The monarch butterfly, which migrates annually over the 3,000 miles from Canada to Mexico, has faced hard times in recent years. Its winter havens in Mexico are threatened by urban growth, and a few wet winters have decimated the butterfly population.
Along the way to Mexico, the butterflies stop to breed, laying eggs on milkweed plants near cornfields. The larvae, or caterpillars, eat the milkweed leaves, eventually turn into butterflies, then take to the air to continue the trip their parents started. It usually takes two generations for a monarch to complete the journey.
Bt corn contains genes from the naturally occurring bacterium Bacillus thuringiensis which produces a protein that kills the corn borer, an insect that can destroy as much as 20 percent of a crop.
"Bt corn essentially comes with a natural insecticide already in it. As the corn borer larvae eat the leaves and stalks of the Bt corn plants, they stop feeding and eventually die after several days," says Dively.
Scientists say pollen from a type of Bt corn known as the Bt 176 can poison monarchs if too much of its pollen lands on milkweed, but the EPA didn't re-register the Bt 176 type, so it will no longer be sold.
Oberhauser, who also published a paper in the Proceedings of the National Academy of Sciences, says Dively's team hasn't looked closely enough at the risks to monarchs.
Oberhauser says because much of Dively's research was done in the lab, it doesn't take into account the pollen-laden anthers (structures that produce pollen) that also blow on to the milkweed. Oberhauser says she isn't certain that monarchs eat anthers, but if they do, they would get a huge dose of Bt pollen.
She also has other concerns. "I think we still don't know the effects of long-term exposure to Bt. Some lab studies may not have exposed them long enough to tell." And even if Bt doesn't kill monarchs at levels found in cornfields, she says, "We don't know how Bt affects factors like monarch reproduction, flight ability and size."
What To Do
To help people understand the complex issues here, the University of Iowa has published questions and answers about Bt corn and Monarchs based on a 1999 study.
For the biotech industry's point of view, click here.
And the University of Kansas has a site devoted to everything you ever wanted to know about the monarch butterfly.