by Jonathan Skinner
The area of forest occupied by the butterflies, once as high at 50 acres, dwindled to 2.94 acres in the annual census conducted in December, Mexico’s National Commission of Natural Protected Areas disclosed at a news conference in Zitácuaro, Mexico.
That was a 59 percent decline from the 7.14 acres of butterflies measured in December 2011.
But an equally alarming source of the decline . . . is the explosive increase in American farmland planted in soybean and corn genetically modified to tolerate herbicides.
The American Midwest’s corn belt is a critical feeding ground for monarchs, which once found a ready source of milkweed growing between the rows of millions of acres of soybean and corn. But the ubiquitous use of herbicide-tolerant crops has enabled farmers to wipe out the milkweed, and with it much of the butterflies’ food supply.
A rapid expansion of farmland — more than 25 million new acres in the United States since 2007 — has eaten away grasslands and conservation reserves that supplied the monarchs with milkweed.