[Marxism] For the Monarch Butterfly, a Long Road Back

Louis Proyect 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

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’s behavior.”

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 
prove catastrophic.

“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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