Herbicide-resistant crops can withstand Roundup, which kills monarchs’ preferred nesting plant.
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.
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