Loss of milkweed habitat puts Monarch butterflies in distress

Many insects cause an instant “yuk” response as they scuttle or fly into our attention zone. Butterflies, however, usually elicit “oohs” and “aahs” as they flit from flower to flower with colorful ostentation.

Befittingly, the orange and black monarch butterfly reigns supreme in this regard, not only for the stained-glass beauty of her wings, but also for her multigenerational migrations that have for decades entranced and intrigued scientists and laymen alike. Those migrations are now threatened as scientists have seen monarch populations plummet from 1 billion to about 33 million during the last decade. People are rallying to protect this insect whose fate has become entwined with human population growth and maintenance.

Part of the monarch’s problem arises because she is a picky eater. She lays eggs on various species of milkweeds—plants in the genus Asclepias that produce chemicals (glycosides) noxious to many animals but chemicals that, when incorporated into the tissue of her young larvae, serve as repellents to potential predators. Because milkweeds are perceived as “weeds” — plants that sometimes compete with corn and other human crop plants—they are disappearing across broad swaths of North America. Saving the monarch becomes an exercise in saving milkweeds by modifying pesticide use, planting more milkweed seeds in appropriate habitat, and educating people to recognize milkweeds as important plants for many pollinators, not just monarchs.

In “Dinosaurs in the Garden,” a book I wrote in 1988, I devoted a chapter to describing the intimate association of insects and flowering plants over geological time using the “milkweed universe” as a prime example. Spend time observing milkweeds and you soon discover they provide food, shelter, and/or habitat for a broad network of living things, including springtails, dragonflies, lacewings, chinch bugs, milkweed bugs, milkweed longhorn beetles, bumblebees, honey bees, moths, ants, aphids, and many more. Milkweeds extract payment for these services by enticing pollinators to visit their aromatic pink flowers and inadvertently pick up pollen in saddlebag-like sacks called pollinia that become clipped to insect legs. These insects insure the milkweed’s long term reproductive success and survival.

Typically, 20 or more species of milkweeds thrived from Canada south to Mexico and on both sides of the Rocky Mountains. Populations of North American monarchs that depended on these milkweeds at some point evolved migratory behavior that led them to move back and forth across the continent, spending part of that time in key refuges in either the forests of Mexico or Southern California.

Now, several factors are shutting down milkweed regeneration. U.S. Fish and Wildlife Service director Dan Ashe said that we are on the verge of losing a “magical migration that spans 3,000 miles for some (monarchs) and multiple generations.”

Causes are multifold and include:

• Transformation of grasslands into farmland with loss of milkweeds through both habitat loss and the use of herbicides

• Colder winters in Mexico that impact forest growth along with logging of existing forests that decreases habitat. Droughts in Texas have also disrupted milkweed growth there.

• Invasive flora and fauna that either impact milkweed growth and/or monarch survival.

• More use of synthetic insecticides with mixed impacts on monarchs and milkweeds.

• Loss of other nectar plants along migration routes for similar reasons.

In search of solutions to the monarch’s demise, President Enrique Peña Nieto of Mexico, President Obama in the U.S. and Prime Minister Stephen Harper in Canada announced this May that they would organize an international task force to address the problem.

The Mexican government has already been dealing with illegal deforestation in the Monarch Butterfly Biosphere Reserve, a 140,000-acre forest preserve that hosts eastern monarchs from November to March. Nieto pledges to strengthen sustainable forest practices in surrounding communal lands.

Ashe plans to increase milkweed habitat, perhaps by planting seeds along major road corridors like Interstate 25 and Interstate 35. The Xerces Society, an invertebrate conservation group (www.xerces.org) has helped form the Monarch Joint Venture (MJV), a partnership between federal and state agencies, non-governmental groups, and academic programs that is also trying to expand milkweed habitat and reduce other threats to monarchs. (See http://monarchjointventure.org/)

The Canadian government is planning to set aside funds for increasing milkweed habitat on farmlands, roadsides and utility corridors. Canada is also trying to protect more monarch staging habitat, where the insects congregate as they prepare to move south.

Paul Opler, an entomologist at Colorado State University who worked on producing the Roger Tory Peterson butterfly field guides, feels that one underappreciated threat to monarchs may be a European paper wasp (Polistes dominula). The wasp first invaded North America near Boston in the 1970s and has since worked its way across the country, preying on many butterfly species. In Colorado, butterfly populations began to nose dive about the turn of the millennium. This roughly coincides with wasp arrival here, but also with spraying for West Nile virus in mosquitoes, so it’s hard to separate the impacts of both events.

The good news is that the monarch’s persona as a pretty, six-legged “Bambi” tends to open hearts and wallets. Another CSU professor, John B. Loomis, who specializes in the economic valuation of natural resources, was the lead economist in a study that showed that people are receptive to the monarch’s plight and will be willing to spend money for potting soil with systemic pesticides, plant more milkweed seeds and other nectar-producing plants, and donate to monarch conservation causes.

E.O. Wilson, the Pulitzer Prize-winning Harvard entomologist and conservationist, has an even bolder plan for preserving the entire non-human fabric of the biosphere that is imperiled by both human growth and the climate change that growth is helping to cause. He proposes a “Half Earth Plan,” outlined recently in an article called “The Wildest Idea on Earth,” written by Tony Hiss in the September 2014 issue of Smithsonian magazine. The general concept is that humans get half the planet and the rest of the living world gets the other half in the form of long, natural N-S trending landscapes that will allow all living things to migrate as climate changes optimal living areas for various species. M.C. Davis, a multimillionaire from Florida, has been working with Wilson to acquire properties that would serve as such corridors.

Monarch migration hinges on the mutation of a single gene in the monarch genome, according to evolutionary biologist Marcus Kronforst at the University of Chicago. The results of his study, reported in the Oct. 1 issue of Nature, indicates that the migration habit arose in North America. Other, non-migratory relatives live in South and Central America. Kronforst and other biologists are eager to learn more about just how this sensitive gene sets in motion unique behaviors that echo across several monarch generations. “If it (migration) disappears,” said Kronforst, “there’s nothing else like it.”