Study ties GMO corn, soybeans to monarch butterfly decline

By JOSEPHINE MARCOTTY, Star Tribune
16 March 2012 Genetically engineered corn and soybeans make it easy for farmers to eradicate weeds, including the long-lived and unruly milkweed. But they might be putting the monarch butterfly in peril. The rapid spread of herbicide-resistant crops has coincided with — and may explain — the dramatic decline in monarch numbers that has troubled some naturalists over the past decade, according to a new study by researchers at the University of Minnesota and Iowa State University. Between 1999 and 2010, the same period in which so-called GMO crops became the norm for farmers, the number of monarch eggs declined by an estimated 81 percent across the Midwest, the researchers say. That’s because milkweed — the host plant for the eggs and caterpillars produced by one of one of the most gaudy and widely recognized of all North American butterflies — has nearly disappeared from farm fields, they found. It is one of the clearest examples yet of unintended consequences from the widespread use of genetically modified seeds, said John Pleasants, a monarch researcher from Iowa State in Ames, Iowa. “When we put something out there, we don’t know always what the consequences are,” he said. Pleasants and Karen Oberhauser, of the University of Minnesota, published their findings online last week in the journal Insect Conservation and Diversity. “It is quite an extraordinary paper,” said Chip Taylor, an insect ecologist at the University of Kansas and the director of research at Monarch Watch, a conservation group. He noted that Oberhauser and Pleasants were able to tie the loss of habitat to a decline in numbers across the country. […] Some scientists have for years wondered whether the use of genetically modified crops is affecting the spring and summer reproduction in this country. Earlier studies suggested that monarch caterpillars would die if they ate milkweed dusted with pollen from another kind of engineered seed known as BT corn. It contains a gene that produces a toxin that kills corn-eating pests. That theory was disproved, but it led scientists to take a hard look at milkweed plants in corn and soybean fields, said Pleasants. “Surprisingly, monarchs use those milkweeds more heavily than milkweed outside [farm fields],” he said. The butterflies lay nearly four times as many eggs on farm field plants as on those in pastures or on roadsides, the researchers said. More important, they also found “that milkweed in the fields was disappearing,” he said. That’s because more farmers are using a new kind of genetically modified seed developed by Monsanto, Roundup-ready corn and soybeans, that contain a gene allowing the plants to withstand Roundup, or glyphosate. That allows farmers to spray their fields without harming the crop. Monsanto, which did not respond to a request for comment, says on its website the seeds help farmers increase yield. Today, it’s used by 94 percent of soybean farmers and 72 percent of corn farmers, according to federal data. […]

Study ties GMO corn, soybeans to butterfly losses