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William and Mary researchers study milkweed to help save monarch butterfly

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The monarch butterfly — perhaps the most recognizable of its kind — is fast disappearing, with population declines of up to 90 percent documented over the last decade.

The most likely culprit?

It’s not disturbances in the monarch’s overwintering sites in central Mexico or extreme weather events. Instead, research suggests it’s because the lowly plant that serves as its key habitat — the common milkweed — is being mowed down, plowed under and poisoned with abandon.

To help stem the monarch’s rapid slide toward extinction and possibly even reverse it, two biologists at the College of William and Mary in Williamsburg embarked this year on a project to sequence the DNA of milkweed plants in hopes that boosting monarch habitat will help the butterfly rebound.

“Understanding patterns of milkweed chemical diversity and milkweed genetic diversity is key to understanding how the monarchs survive,” said researcher Joshua Puzey.

Puzey and his colleague, ecologist Harmony Dalgleish, are collecting milkweed leaf samples and even some insects that were mailed to them by 183 volunteer citizen-scientists from 28 states across the country, including 17 in Hampton Roads.

The volunteers are part of a larger and ongoing Monarch Larva Monitoring Project developed at the University of Minnesota, but they pitched in this season to help with local sequencing effort.

Puzey and Dalgleish will extract and sequence DNA from the samples to understand milkweed relatedness across its wide range.

A better understanding of milkweed genetics, Puzey said, will help inform where they should sample monarchs going forward, as well as assist with habitat replanting efforts to try to help them reestablish.

Milkweed loss

While milkweed plants aren’t endangered, he said, their populations have declined significantly in recent years, displaced by agriculture and development, leading to an even more dramatic decline in the monarch.

Two studies of milkweed loss in the Midwest explored that link.

Biologists at Iowa State University and the University of Minnesota found a 58 percent drop in milkweed in the landscape corresponding with an 81 percent plunge in monarch production between 1999 and 2010.

“Taken together,” the researchers wrote in 2012, “these results strongly suggest that a loss of agricultural milkweeds is a major contributor to the decline in the monarch population.”

They attribute the double whammy to a rise in herbicide use as farming of genetically modified corn and soybeans increases.

Yet another study of monarch butterfly populations in the Midwest, this time published by British researchers in 2014, found a 90 percent decline linked to a reduction in milkweed host plants. They, too, attribute it to “increasing adoption of genetically modified crops and land-use change, not from climate change or degradation of forest habitats in Mexico.”

Reducing that plant loss, they said, is a “top conservation priority” to lower the risk of monarch extinction.

The monarch

Few would argue the iconic butterfly isn’t worth saving.

“Monarchs are incredible,” said Dalgleish. “I think it’s the migration that’s so captivating, because the adult butterflies will fly maybe even as far as southern Canada all the way down to that wintering site in central Mexico. The adults live there and spend the winter there and then they’ll migrate back up and lay their eggs on milkweed.”

Not every adult monarch makes that intercontinental journey, she said. For many, it takes multiple generations, flying first from Mexico to the deep South to lay eggs that will become butterflies that will fly even farther north — perhaps to Virginia — to repeat the cycle.

Some will linger here, while others will journey farther still, perhaps as far as Canada. Finally, a generation known as “super monarchs” will emerge, she said, and they will be the ones to flutter thousands of miles south during the great fall migration to the wintering grounds in Mexico.

“That just boggles my mind,” said Dalgleish.

Scientists still don’t completely understand how the super monarchs manage it, she said.

Monarchs have distinctive tawny orange wings, with black margins and vein patterns. The wingspan typically runs 4 inches.

In North America, the population is largely split into eastern and western populations. It’s the eastern group that makes the Canada-Mexico migration, while the western tends to overwinter in California.

The butterfly has evolved to adapt to its host plant, thriving on compounds the milkweed produces that are toxic to other animals.

“While eating the milkweed plants, they actually become toxic, themselves,” said Puzey. “So basically their bright coloration is a warning to predators saying, ‘Don’t eat me or you’re going to get toxic compounds and get sick.’ “

Restoration efforts

The Monarch Larva Monitoring Project began about a decade ago, enlisting citizen-scientists to venture in the field to count monarch eggs and larva. Registration and training videos are available at http://www.mlmp.org.

Puzey and Dalgleish were given permission to approach project volunteers for milkweed samples, and are also asking local residents to join in. They can be contacted by email at milkweedgenetics@gmail.com.

The milkweed plant might not have the visual appeal of a day lily or an iris, they said, but homeowners might consider adding some to their gardens to help the monarchs.

“The green, leafy plant isn’t much to look at, and the flowers aren’t particularly spectacular,” Puzey said. “A lot of people will just cut them down. I like them.”

Milkweed growing along roadways or public areas are often routinely mowed down, too, he said, “so all that habitat is lost.”

The plants are more common as you drive west toward the Piedmont, Dalgleish said, and national battlefields such as Yorktown are good places to find them because they require open, sunny areas.

More organized replanting efforts are underway at local schools and through chapters of Virginia master naturalists.

The U.S. Fish & Wildlife Service has allocated $2.2 million toward a monarch conservation fund, to restore 200,000 acres of monarch habitat, to support schoolyard projects and pollinator gardens and other restoration efforts. For more information, go to http://www.fws.gov/savethemonarch.

Dietrich can be reached by phone at 757-247-7892.