Monarchs butterflies’ decline correlated to increased plantings of herbicide tolerant GM crops and overuse of glyphosate (RoundUp) herbicide.

Twelve years ago, a study found that genetically modified Bt corn was lethal to monarch butterflies; recent research shows that another type of GM crop is even more damaging to the beloved insect.

“What’s going on down there is a disaster”

A recently published study says that increasing acreage of GM Roundup Ready (RR) corn and soybeans is a major cause for declining populations of monarch butterflies in North America. The paper, published in the journal Insect Conservation and Diversity, says that increased use of glyphosate herbicide with RR GM crops in the Midwest is killing milkweed plants, which monarchs rely on for habitat and food.

Chip Taylor, an insect ecologist at the University of Kansas and co-author of the paper, told the New York Times, “This milkweed has disappeared from at least 100 million acres of these row crops. Your milkweed is virtually gone.”

The paper documents that populations of monarch butterflies in central Mexico, where they migrate to in winter, have declined over the past 17 years, reaching an all-time low in 2009-2010.

Lincoln P. Brower, an entomologist at Sweet Briar College and co-author of the paper, told Wired magazine: “What is going on on the ground down there is a disaster.”

Monarch butterflies migrate from the United States to Mexico each year, traveling some 4000 miles.

Taylor and Brower both criticized a recent paper by Andrew K. Davis, an assistant research scientist at the University of Georgia, which didn’t find a significant decline in monarch populations. Davis analyzed monarch populations in Cape May, N.J., and Peninsula Point, Michigan. Brower said those are minor sites that would not reflect the true status of monarch populations. “His paper is not representative of the big picture (of overall monarch populations), which is Mexico.”

“Bigger threat than Bt corn”

While the paper lists several other factors, such as deforestation in Mexico, contributing to declining monarch populations, Taylor says the proliferation of RR crops and the overuse of glyphosate is the major cause.

“This is the one main factor that has happened,” he says. “You look at parts of the Midwest where there is a tremendous use of these crops and you see monarch populations dropping. It’s hard to deny the conclusion.”

Taylor has been warning about the negative impact of RR crops on monarchs since writing a blog about it in 2001. “I’ve always thought they were a bigger threat to monarchs than Bt corn.”

Taylor says the monarchs’ decline accelerated around 2003 when herbicide tolerant GM crops accounted for nearly 50% of all corn and soybeans. That number has increased to more than 80% in the last two years.

“Once herbicide tolerant GM crops reached 50%, we saw a significant impact on monarch populations,” he says.

Next>> The RoundUp “Biodiversity Armageddon” and how biotech companies mislead the public

Image Credit: Creative Commons photo by _PaulS_

