A graph, or two, is sometimes worth more than 10,000 words. This chart, sent to me by monarch researcher Chip Taylor, shows the rise in Roundup ready corn and soybeans along side the decline in monarchs counted on their winter grounds near Mexico City. He was responding to a story published Saturday about a new study that showed an 81 percent decline in the reproduction of monarchs since the advent of herbicide resistant corn and soybeans. Turns out they work pretty well -- milkweed has virtually disappeared from agricultural fields in the Midwest, the researchers said.
The green line is monarchs -- the red is the percent of farms planted with herbicide tolerant seeds.
Some researchers say they are not entirely convinced because the latest study, by scientists at the University of Minnesota and Iowa State University, used a lot of extrapolation in their analysis. But Taylor, who is the scientific director of Monarch Watch, a conservation group, and a professor at the University of Kansas, says that the relationship is unequivocal.
"There have been a significant decline in the over wintering monarch population since 2003. This decline is related to the adoption of herbicide tolerant row crops which first began in 1996. ... By 2004 the adoption of corn and soybeans genetically modified to resist glyphosate exceeded 51%. The adoption rate by 2010 was 81% (see figure). Milkweeds are now scarce in this formerly productive habitat. Overall, the amount of habitat lost due to the adoption of these crops may exceed 100 million acres."