Published by Communications and Public Affairs (519) 824-4120, Ext. 56982 or 53338
September 20, 2001
GM corn not harmful to Monarch, study finds
An extensive two-year research project by University of Guelph and American scientists may put an end to the ongoing debate on whether genetically modified (GM) corn is harmful to the monarch butterfly.
A series of studies headed by Prof. Markham Sears, Department of Environmental Biology, and scientists at a number of U.S. institutions is set to be published this week in the Proceedings of the National Academy of Science in Washington, D.C. The studies were conducted at various locations across Ontario and North America’s corn belt in both fields and laboratories. They examined a range of issues associated with GM corn, including toxicity and exposure rates. All studies supported the conclusions: risk of GM corn pollen to the monarch butterfly is negligible.
“The risk is so small that it is almost not even there, almost impossible to measure,” said Sears, who worked with Guelph graduate students Diane Stanley-Horn and Heater Mattila on the collaborative research. That finding is in direct contrast to previous studies that claimed monarch caterpillars were killed or severely affected by pollen from GM corn. The Guelph results were also confirmed by a separate study at the University of Illinois that reached a similar conclusion.
Bt corn, as it is commonly called, has been altered by the transfer of genes from the naturally occurring soil bacterium Bacillus thuringiensis to corn plant cells. It does not affect humans or other animals, but prevents a crop-damaging caterpillar called the European corn borer by producing a toxic protein in the green tissues of the corn plant.
Monarch butterflies face many risks, including bad weather, deforestation, spraying of milkweed with herbicides, use of insecticides and even collisions with vehicles, Sears said.
“For example, there was an early frost last winter in Mexico, where monarchs hibernate, that killed about two million of the 10 to 20 million monarchs in North America. And when I was driving into the country, I ran into two butterflies with my car, so multiply that by the number of cars on the road throughout the corn belt. My point is that all risks should be considered in comparison with that from Bt corn pollen.”
Sears’s studies found that only a small portion of the monarch population comes into contact with pollen from any type of corn, let alone pollen from Bt corn. In addition, field trials in five locations throughout the corn belt and Ontario confirmed that the levels of pollen on milkweed in and around cornfields had no effect on monarch caterpillars. About 90 per cent of a cornfield’s pollen falls within five metres of the field’s edge and rarely accumulates in enough concentration to affect monarch larvae.
“The combination of two important factors, the low level of toxicity of pollen and the small likelihood of exposure to pollen, leads us to conclude that risk is negligible,” Sears said. He adds that the chance of a caterpillar being exposed to toxic pollen from Bt corn is less than one per cent. Previous studies suggested a harmful link between Bt corn pollen and monarch butterflies did not take these factors into consideration, he said. “When comparing risks, it’s important to compare benefits as well,” he said. “Bt corn reduces the use of insecticides and prevents the corn borer from invading the ear of the corn and releasing a fungi that is far more toxic than Bt corn pollen.”
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