[Marxism] For the Monarch Butterfly, a Long Road Back
lnp3 at panix.com
Tue Nov 18 08:28:31 MST 2014
NY Times, Nov. 18 2014
For the Monarch Butterfly, a Long Road Back
By LIZA GROSS
Dara Satterfield hadn’t planned to conduct experiments at the Texas
State Fair, but that is where her study subjects showed up last month.
She was still in Georgia when they arrived, so she hurriedly packed her
car, then drove all night. As she pulled into the fairgrounds in Dallas
the next morning, they were feasting on nectar-filled blossoms of
frostweed alongside the Wild West Pet Palooza.
The hungry travelers, like most monarch butterflies that migrate from
breeding grounds in the northern United States and southern Canada, had
stopped in Texas to consume enough calories to power the last leg of
their flight to the oyamel fir forests of central Mexico and survive
five months overwintering there.
So many monarchs blanketed the frostweed that Ms. Satterfield, a
27-year-old doctoral student at the Odum School of Ecology at the
University of Georgia, allowed herself to hope that one of the world’s
most celebrated migrations could be revived.
Less than 20 years ago, a billion butterflies from east of the Rocky
Mountains reached the oyamel firs, and more than a million western
monarchs migrated to the California coast to winter among its firs and
eucalypts. Since then, the numbers have dropped by more than 90 percent,
hitting a record low in Mexico last year after a three-year tailspin.
Preliminary counts of migrants this fall are encouraging. “But we’re
definitely not out of the woods,” said Ms. Satterfield, who studies
human effects on migratory behavior. “One good year doesn’t mean we’ve
recovered the migration.”
To make matters worse, she and her graduate adviser, Sonia Altizer, a
disease ecologist at Georgia, fear that well-meaning efforts by
butterfly lovers may be contributing to the monarch’s plight.
In recent years amateur conservationists have sought to replenish
drastic declines in milkweed, the only plant female monarchs lay eggs
on. But the most widely available milkweed for planting, the scientists
say, is an exotic species called tropical milkweed — not the native
species with which the butterflies evolved. That may lead to unseasonal
breeding, putting monarchs at higher risk of disease and reproductive
Unlike most migrating species, monarch butterflies employ an improbable
strategy that splits their round-trip migration between generations. So
their life cycles must be intricately synchronized with those of the
milkweed on which they lay their eggs.
Monarchs returning from Mexico reach the Southeast soon after native
milkweeds appear in spring, producing the first of up to three
generations that breed on new milkweed through summer. When the
perennials start dying back in the fall, a final generation of
butterflies typically emerges in a sexually immature state. Rather than
reproduce when food is scarce and caterpillars might freeze, they fly to
Mexico, to wait out the winter.
“The tiny creatures that engage in this big, beautiful migration have
never seen the sites in Mexico before and somehow know where to go,” Ms.
Satterfield said. “It’s incredible.”
But in the Midwest, which produces half of Mexico’s wintering monarchs,
the scores of wild milkweed species among grasslands and farms are fast
Nearly 60 percent of native Midwestern milkweeds vanished between 1999
and 2009, the biologists Karen Oberhauser and John Pleasants reported in
2012 in the journal Insect Conservation and Diversity. The loss
coincided with increased applications of the weedkiller Roundup on
expanded plantings of corn and soybeans genetically altered to tolerate
the herbicide. Meanwhile, monarch reproduction in the Midwest dropped
more than 80 percent, as did populations in Mexico.
With the loss of native milkweeds that die in the fall, monarchs are
encountering tropical milkweeds that are still thriving.
“There’s this huge groundswell of people planting tropical milkweed, and
we don’t know what it’s doing to the butterflies,” said Francis X.
Villablanca, a biology professor at California Polytechnic University.
“We’re all in a rush to figure it out.”
Dr. Altizer fears that when monarchs encounter lush foliage in the fall,
they may become confused, start breeding and stop migrating.
“It’s sad, because people think planting milkweed will help,” she said.
“But when milkweed is available during the winter, it changes the
Butterfly enthusiasts shouldn’t feel bad for planting tropical milkweed,
monarch researchers say. But they should cut the plants back in fall and
winter. Or even better, replace them with natives. There are native
plant societies across the country that can offer advice.
Recent work by Dr. Oberhauser’s lab found that some migrating monarchs
are laying eggs in the Southeast when they find tropical milkweed.
Last December, Dr. Villablanca found breeding in overwintering sites in
California. “We’re in shock by the number of monarchs that are coming
through and laying eggs,” he said.
The reports are worrisome because nonstop breeding on the same plants
can unleash a devastating parasite called OE, for Ophryocystis
Adult monarchs infested with the parasite can carry millions of spores
that contaminate milkweed and kill foraging caterpillars. Mildly
infected monarchs often can’t fly or reproduce normally, and die early.
It was in the late 1990s that Dr. Altizer, then Dr. Oberhauser’s student
at the University of Minnesota, first showed that persistent breeding
favors the parasite. In lab experiments, she fed monarchs either
tropical milkweed collected from sedentary colonies in southern Florida
or native species picked in Minnesota. Tropical milkweed produced much
higher infection rates.
She has found similar results in the wild. Her team sampled thousands of
monarchs at winter-breeding sites along the Gulf of Mexico and at
summer-breeding sites to the north with help from the citizen science
group Monarch Health. Colleagues sent samples from more than 2,000
monarchs at Mexican wintering sites. Those that spent the winter
breeding on tropical milkweed had significantly higher levels of parasites.
Since 2002, the prevalence of OE among eastern migratory populations
increased nearly threefold, Dr. Altizer has found. She worries that
migrants may pick up parasites as they pass through winter-breeding
colonies — and even start breeding themselves.
Work from Dr. Oberhauser’s lab suggests that this could happen.
Her team reared monarchs from eggs collected in Minnesota under
conditions that yield nonreproductive butterflies, then collected
roosting fall migrants from Texas. They assigned butterflies to cages
with native milkweed, no milkweed or tropical milkweed. No mating
occurred in milkweed-free cages.
But a fraction mated when milkweed was present, whether tropical or
native. In field experiments, females preferred laying eggs on tropical
milkweed in the fall, presumably because it was fresher.
In her own field work, Ms. Satterfield has found far more caterpillars
on tropical plants in winter than is typical on natives in summer. The
close quarters place them at high risk of serious infection, assuming
they don’t starve or freeze first.
Not all monarch experts worry about tropical milkweed. “Monarchs utilize
an immense landscape in the Eastern U.S., and this plant constitutes a
tiny, tiny portion of the milkweeds encountered by monarchs returning in
the spring,” said Chip Taylor, an ecologist at the University of Kansas
who directs the conservation group Monarch Watch. “Should they be there?
Probably not. But will they do immense harm? Probably not.”
If monarch populations keep falling, the coastal regions could become
more important, Dr. Oberhauser said. Migration can limit disease by
weeding out the sick and allowing butterflies to leave contaminated
plants behind. If year-round milkweed changes the migratory behavior of
enough monarchs, she said, “it could have really far-reaching impacts.”
So far, evidence that monarchs stop migrating to breed is indirect.
“People plant tropical milkweed and then we see monarchs reproducing
when they should be migrating or overwintering,” Dr. Altizer said.
“There needs to be more experimental work done.”
And that is why Ms. Satterfield drove all night to catch butterflies in
The monarchs she collected in Dallas and at another site without
tropical milkweed will help her assess the plant’s effects at four
coastal sites where it is common. She plans to analyze chemicals in the
butterflies’ wings to distinguish migrants from residents based partly
on what they ate as caterpillars. The analyses will show if migrating
monarchs pass through the sites. If they interact with resident
breeders, it could help explain why disease is increasing among eastern
To figure out if migratory monarchs are breeding at tropical milkweed
sites, Ms. Satterfield will look for eggs in females and mating behavior
in males. She will know if they also abandoned the migration if
individuals tagged last month are still there when the migration ends.
No one disputes that loss of milkweed habitat remains the monarchs’
biggest threat. But if the population gets smaller, risks once
considered less important — like severe weather and disease — could
“We’ve learned the hard way with migratory bison and whooping cranes
that once we lose a migration, it is close to impossible to bring back,”
Ms. Satterfield said. “Protecting the great North American journey of
the monarch is crucial now, while we still have a chance.”
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