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article imageLowly milkweed may be key to saving the Monarch

By Martin Laine     Jun 6, 2014 in Science
It may not be a startlingly beautiful plant, nor is it of much use to modern man, but the once-ubiquitous milkweed is critical to the life-cycle of the Monarch butterfly. New research suggests it may be even more important than previously thought.
It may be critical to the survival of the entire species.
“Our work provides the first evidence that monarch butterfly numbers in eastern North America are most sensitive to changes in the availability of milkweed,” said Prof. Ryan Norris of the Dept. of Integrative Biology at the University of Guelph, in an article on the Science Daily website.
Norris conducted the study with lead author Tyler Flockhart, a post-doctoral fellow at the University of Guelph, and scientists from the Commonwealth Scientific and Industrial Organisation in Australia. Their findings were published in the Journal of American Ecology.
Monarch populations have been on a steady decline over the past quarter century, and reached the lowest point ever recorded two years ago.
The regal-looking butterfly is perhaps best known for its remarkable annual migration from the fields of the United State and southern Canada to a relatively small forested area of central Mexico, covering distances of up to 2,500 miles, one of the longest known insect migrations.
When the decline in Monarch populations began to be noted, early attention was focused on logging operations in their Mexican winter habitat. Conservation efforts slowed the amount of logging, though some illegal logging persists in the region.
“The protection of overwintering habitat has no doubt gone a long way toward conserving monarchs that breed throughout eastern North America,” Flockhart said. “However, our results provide evidence that there is now another imminent threat.”
Still, the decline has continued, and Norris and his colleagues began studying the migration patterns to look for other clues to the decline.
It’s long been known that the milkweeds are the only plants Monarchs visit. The adults feed on the nectar of the flowers, they lay their eggs on the leaves, and after they hatch, the larvae feed on the leaves.
Monarchs on their way to Mexico pass through the vast agricultural area known as the Corn Belt, and that, too, is where the most milkweed has traditionally been found. But modern industrial farming methods and the use of genetically-modified, herbicide-resistant crops have altered the landscape, and milkweed has experienced a 21 percent decline between 1995 and 2013.
The decline in milkweed corresponds closely to the decline in monarch populations over the same period, the study shows.
“Reducing the negative effects of milkweed loss in the breeding grounds should be the top conservation priority to slow or halt population declines of the monarch in North America,” Flockhart said.
More about Monarch butterfly, Milkweed, Migration
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