Renewed Monarch Decline After 'Good Intentions' Go Awry

Efforts to save the declining monarch butterfly across the United States may have severely backfired, with many gardeners unwittingly trapping and exposing these near-endangered insects to harmful parasites.

Each year, by the end of autumn, millions of Monarch butterflies in the northeastern United States and Canada start to wing their way south in a stunning 2,500-mile journey. They traditionally spend their winter among the volcanic mountains of Central Mexico, which are spotted with ideal fir tree habitats.

However, past logging activity in these protected regions has begun to shrink the monarch wintering habitat, and fewer and fewer butterflies have been seen making their annual migration.

In fact, just last January the World Wildlife Fund (WWF) revealed that nearly 44 percent of the forestland occupied by monarchs in and near Mexico's Monarch Butterfly Biosphere Reserve during 2012's winter months had disappeared by 2013.

Worse still, the 2013 migrating population boasted the lowest count of monarchs since 1993 (the year scientists started to monitor monarch butterfly colonies), according to research released by the WWF-Telcel Alliance and the Mexican government.

Many US butterfly watchers have made a habit of traveling to popular migration routes to watch flocks of these brilliant orange, yellow, and black butterflies nearly blot out the Sun as they flutter into Mexico by mid-November. This helped news of their decline spread like wildfire, as these stunning sightings appear to have grown less common each year.

Back in December it was even reported by the US Fish and Wildlife Service (FWS) that the butterflies had declined by a whopping 90 percent over the past 20 years, making them a strong contender to be granted federal protections under the Endangered Species Act. (Scroll to read on...)

In the wake of all this, butterfly buffs started calling for action, asking everyday gardeners to break out their spades and start planting milkweed - a pretty and easy-to-grow flower that butterflies love. It also grows well in the climates of the southern United States.

The hope was that monarchs on their annual journey would see these milkweed gardens and decide to start their holiday early, wintering in backyards along the Gulf Coast and in Texas, in addition to the Mexican fir forests.

And unfortunately, this idea seems to be working. But why is that unfortunate?

The only species of milkweed widely available in the United States is Asclepias curassavica - an imported tropical rendition of the butterfly-friendly plant. These plants don't die off in winter like their northern-born cousins, and can serve as a place for monarchs to feed and lay their eggs year-round. The result is that many monarchs have stopped migrating altogether.

And while that is bad news for sight-seers, it will at least give the monarch populations a chance to recover from decline, right?

Wrong. According to a study recently published in the journal Proceedings of the Royal Society B, monarch populations that spend their winters in southern US gardens are up to nine times more likely to become infected with a dangerous parasite, compared to butterflies who migrate all the way down to Mexico.

That's because milkweed can naturally host a protozoan parasite called Ophryocystis elektroscirrha (OE). If a monarch caterpillar takes its meals from an infected plant, it will wind up ingesting these tiny parasites as well, and when it hatches from its chrysalis, it will be covered in debilitating spores.

Infected butterflies have far less energy than their healthy counterparts, don't live nearly as long, and are less likely to successfully reproduce. What's worse, if they try to migrate, they are doomed to fail, researcher Dara Satterfield explained to Science magazine.

This is why the migration is a necessary thing, she said, as it "weeds out some of the sick monarchs each year." (Scroll to read on...)

As winter presses on and northern milkweed dies, these butterflies are forced to get moving, and most adults who are infected wind up never making it to Mexico. When the butterflies return to the northern US in the spring "they start over fresh" with new, clean milkweed, Satterfield added.

And this is why the good intentions of gardeners may be causing even more trouble for the delicate insects, where tropical milkweed is tricking the monarchs into abandoning their migratory ways, and keeping a harmful OE presence strong.

According to the study, many new breeding sites in the southern US already boast a 100 percent infection rate. That's exceptionally bad news even for monarchs returning from the Mexican forests as they may be tempted to make a pit stop, or end their journey entirely, in someone's infected backyard.

So what can we do? Karen Oberhauser, a conservation biologist at the University of Minnesota, argues that once again, backyard gardeners need to rally. Awareness of this new milkweed problem, she told Science, is the first step, and second would be to have these gardeners replace their tropical plants with native northern milkweeds.

"It's a problem we can solve," she said, emphasizing that the good intentions of gardeners can still be put to good use.

Having trouble finding native milkweed seeds? They are still not nearly as common as the tropical variety, but the Xerces society, in support of the North American Monarch Conservation Plan, has recently taken action in collaboration with the native seed industry, the USDA-NRCS Plant Materials Program, and various community partners to create sources of milkweed seed in California, the Great Basin, Arizona, New Mexico, Texas, and Florida.

You can use the milkweed seed finder here to find seed sources in your state.

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