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90% drop in monarch butterflies linked to loss of milkweed

Dead monarchs in Mexico.
Dead monarchs in Mexico.
Photo by Getty Images/Getty Images

United States Canada and Mexico have formed a pact to restore milkweed in an effort to save the monarch butterfly.

According to researchers at the University of Guelph in Canada, factors linked to the drop in migratory monarch butterflies to the loss of milkweed, especially in certain breeding grounds for them in America’s Midwestern states due to the high use of herbicides in the Corn Belt region and other “high-intensity agricultural parts of the country.

"We're losing milkweed throughout Eastern North America, but what we found out is milkweed loss specifically in the Midwestern U.S. is likely contributing the most to monarch declines," noted study co-authors Tyler Flockhart and Ryan Norris, a professor in the University of Guelph's Department of Integrative Biology, along with members of Australia's national science agency. In fact they reported a “21% decline in milkweed plants in the region between 1995 and 2013.”

The plant is important for the distinct orange and black butterfly species because the insect lays its eggs on it. It is also the only group of plants that monarch caterpillars feed on before developing into butterflies," Flockhart stated. "Reducing the negative effects of milkweed loss in the breeding grounds should be the top conservation priority to slow or halt future population declines of the monarch in North America, with the populations in Mexico alone dropping all the way down to approximately 33.5 million this year from an “annual average of about 350 million.”