Laboratory Equipment has some bad news for butterflies:
After steep and steady declines in the previous three years, the black-and-orange butterflies now cover only 1.65 acres (0.67 hectares) in the pine and fir forests west of Mexico City, compared to 2.93 acres (1.19 hectares) last year, says the report released by the World Wildlife Fund, Mexico’s Environment Department and the Natural Protected Areas Commission. They covered more than 44.5 acres (18 hectares) at their recorded peak in 1996.
Lincoln Brower, a leading entomologist at Sweet Briar College in Virginia, says that “the migration is definitely proving to be an endangered biological phenomenon.”
“The main culprit,” he write in an email, is now genetically modified “herbicide-resistant corn and soybean crops and herbicides in the U.S.,” which “leads to the wholesale killing of the monarch’s principal food plant, common milkweed.”
While Mexico has made headway in reducing logging in the officially protected winter reserve, that alone cannot save the migration, writes Karen Oberhauser, a professor at the Univ. of Minnesota. She notes that studies indicate that the U.S. Midwest is where most of the butterflies migrate from.
“A large part of their reproductive habitat in that region has been lost due to changes in agricultural practices, mainly the explosive growth in the use of herbicide-tolerant crops,” Oberhauser says.
Extreme weather — severe cold snaps, unusually heavy rains or droughts in all three countries — have also apparently played a role in the decline.
But the milkweed issue now places the spotlight firmly on the U.S. and President Barack Obama, who is scheduled to visit Mexico on Feb. 19, with events scheduled for Toluca, a city a few dozen miles from the butterfly reserve.