Across the Midwest, farmers have all but eliminated the scourge of milkweed among their crops through the use of genetically modified corn and soybeans resistant to the herbicide Roundup. This allows farmers to spray the chemical to eradicate weeds, including milkweed without harming their crops. But the one-two punch of GMO crops and the powerful herbicide may have caused collateral damage-- a drop in Monarch butterfly populations that depend on milkweed for survival.
Milkweed is an integral part of the Monarchs’ lifecycle as they lay their eggs on the weed and their larvae eat it. “This milkweed has disappeared from at least 100 million acres of these row crops,” said Dr. Taylor, an insect ecologist at the University of Kansas and one of the study authors. “Your milkweed is virtually gone.”
Say good-bye to Monarchs?
The researchers base their evidence that monarch populations are declining on the size of the area occupied by monarchs in central Mexico, where many of them spend the winter. This area has been shrinking over the last 17 years.
Other Midwest researchers with the University of Minnesota and Iowa State University cite other evidence for a decline--the number of monarch eggs in fields across the Midwest. By their count Monarch egg production has decreased significantly and point to the loss of milkweed resources available to them as the cause.
In other parts of the country, monarch populations are not showing a decrease in numbers, and it is unclear whether the biotech crops are having an effect there. Annual censuses of adult monarchs taken each fall at Cape May, New Jersey and Peninsula Point, Michigan as well as parts of Maryland did not show a decline.
Midwest is the primary incubator for Monarchs.
Despite the mixed Monarch population reports, entomologists are still concerned. According to a 2001 study, the sheer amount of farmland in the Midwest accounts for a vast majority of monarch births. That study estimated that in Iowa, farms produced 78 times the number of monarchs as nonagricultural sites, and in Wisconsin and Minnesota, 73 times as much.
Meanwhile, the amount of milkweed on farms in Iowa declined 90 percent from 1999 to 2009, according to Robert G. Hartzler, an agronomist at Iowa State. His study, published last year in the journal Crop Protection, found milkweed on only 8 percent of the corn and soybean fields surveyed in 2009, down from 51 percent in 1999.
Scientists say it is not surprising that suppressing weeds would have an effect on insects. The National Academy of Sciences discussed this in a 2007 report on bees and other animals that pollinate crops. The report cited a British study that found fewer butterflies in fields growing genetically engineered beets and canola than in fields growing nonengineered crops. v So, should weeds on farms be protected?
“There’s a change in agricultural thinking, because the weed-free field was the gold standard,” said May Berenbaum, head of entomology at the University of Illinois.
Most insect experts acknowledge that farmers would be unwilling to give up herbicide-tolerant crops, so other ideas have been tossed about to set aside conservation areas in the Midwest to grow milkweed for Monarchs.
Dr. Taylor of Monarch Watch had an ironic request of biotechnology companies. “I would implore them to develop a Roundup-resistant milkweed,” he said.
To learn more about GMOs, read our latest newsletter: You’re Already Eating Genetically Modified Foods: Are They Safe?
Source:
New York Times