For monarch butterflies, Florida’s ‘cesspool’ of infection may leave many too weak to migrate
Every year, flocks of majestic monarch butterflies fly on a massive fall migration from the northern United States to a small region near Mexico City - with the exception of an idiosyncratic population that deviates to Florida.
Why some butterflies break off towards the Sunshine State is one of the many mysteries of monarchical behavior, but an emerging scientific debate revolves around the thousands of South Florida enthusiasts who created butterfly gardens to revive an iconic and endangered species. Some scientists believe that the long-standing, naturally occurring Florida diaspora is unnaturally made to lazy year round rather than migrate due to a widespread tropical plant.
Worryingly, if monarchs do not migrate, they will accumulate a wing-deforming parasite called OE.
"South Florida is a cesspool of infected monarchs," said Andy Davis, an assistant monarch ecology researcher at the University of Georgia. "Take any monarch there and he will have OE."
There is hope that a switch to native milkweed planting could transform the region from a parasite peninsula into a natural butterfly resort.
"A complicated story"
The full benefits of tropical milkweed, a predominant import in South Florida gardens, are still being researched and are just one of several questions about the monarchs roaming the state - some of them the subject of considerable uncertainty and ongoing debate.
"Florida's role in monarch migration is a complicated story," said Jaret Daniels, regional expert and curator on lepidoptera (i.e., moths and butterflies) at the University of Florida Museum. Much like the human population of South Florida, he said, monarchs seem like a mishmash.
A Florida monarch butterfly caterpillar nibbles on tropical milkweed, a commonly planted butterfly garden plant that many scientists believe could alter the migration patterns of monarch butterflies
There are "South Florida residents" who never emigrate and who spend their days drinking nectar in Milkweedville year-round. There are “real migrants” who only cross Florida on their way to Mexico. There are some who “fall away” during migration and form butterfly enclaves. Others are fleeing to the Caribbean, and scientists don't think they're coming back. What is especially amazing, Daniels said, is why some adopt these different lifestyles and how much interaction there is between the groups.
Here is a indicative measure of the mystery of the Florida monarchs: Karen Oberhauser, director of the University of Wisconsin-Madison arboretum and chair of the Monarch Joint Venture Steering Committee, is a leading authority on their migration patterns. "When we run monarchical population models, we've often cut Florida off the pan," she said. South Florida is just too confusing.
Monarchs flying to Florida isn't new. But their persistent and sickly state of laying eggs on non-native milkweed could be.
Florida actually has many native species of milkweed, but fewer than a handful of the roughly 20 in the wild are available from commercial nurseries. Instead, tropical milkweed from Central America has gained popularity because it's easy to grow, attracts tons of monarchs, and blooms a lovely burst of orange and red flowers.
A monarch butterfly that nests on Marsh Milkweed, a native Florida species that has pink flowers.
"According to recent research, monarchs tend to stop migrating when they encounter tropical milkweed," said Daniels. The theory is that the flowers of native milkweed, which disappear in winter and reappear in warm temperatures, ring like bells that ring the monarchs to fall asleep and wake up to migrate.
But tropical milkweed is not dying back in Florida. Instead, it blooms year-round, preventing monarchs from receiving the signals to hibernate or move north in the spring.
While Mexican monarchs spend their winter celibate and snuggle up in the cold mountains for warmth, Florida monarchs have an incessant bacchanal of milkweed, sex, and sunshine.
Sounds good, but it isn't.
"The South Florida population has been around a long time," said U-Madison's Oberhauser, "but they're probably unhealthy."
It relates to high rates of infection by OE, the parasite on milkweed. OE is ubiquitous on both native and non-native plants. However, nature has one way of purifying it from the population: migration. Monarchs infected more slowly cannot survive the long flight and usually leave behind healthy specimens in the end. "Trying to migrate with OE is like trying to run a marathon on one leg," said UGA's Davis. The clean marathon winners at the end can reproduce in the prairie lands in the north and in the Midwest.
But Florida non-wandering monarchs are not cleansed. Instead, they constantly pass parasites on to one another. Worse still, they can spread OE to the rest of the monarch population as well.
"Florida hasn't always been a breeding ground for disease," said Davis. “But OE is spreading like wildfire because of the planting of tropical milkweed. Now South Georgia is becoming a hotbed and East Louisiana. It is a growing problem and is led by Florida. "
Billed South Florida monarchs for the Monarch Health project to test for OE parasites.
There are some who argue that tropical milkweed is perfectly fine for monarchs and point to unresolved contradictions. For example: some native Florida silk plants bloom year-round, as do tropical silk plants, but do not appear to be harmful. Tropical milkweed in northern Mexico also supports monarch migration well. Perhaps the problem is limited to the southeast, where the combination of heat, humidity, tropical milkweed, and the distance from Mexico encourage butterflies to frolic in parasite land.
After interviewing 12 experts for their opinions, Davis concluded: "No respected monarchist scientist recommends that people plant or use tropical milkweed."
“If I could tell the people of Florida one thing, it would be that we have to break the desire to have monarchs in winter. Often times people see caterpillars on tropical milkweed and think, “Wow, that's great. I'll help! ’Then that big wanker comes from a scientist and tells them not to plant it. But the problem is, you have to look at the entire life cycle, on science. "
Should you be here?
A migration that stretches for 2,000 miles and crosses multiple countries is usually reserved for large animals or soaring birds, not an insect that weighs as much as a dollar bill. That alone made this orange wonder one of the most popular insects in the world.
But with legions of monarch aficionados in Florida planting milkweed to aid the species, the question naturally arises: should monarchs be here? After all, Mexico City is a far cry from Miami.
Monarchs fill the sky in Mexico, the winter stop on their migration from North America.
"Most of the research on monarchs takes place in the Midwest," said Daniels of UF. “Florida didn't focus on much at all. We don't know the history of what happened here. ”Only recently have further studies attempted to shed light on why some monarchs end up so far from their ancestral territories in Mexico.
A 2018 study by Hannah Vander Zanden, Assistant Professor of Animal Movement and Biology at the University of Florida, shed a fascinating light on the subject. Her research included taking the wings of victims of Florida monarchs, setting them on fire, and using ions and magnets to read the smoke and determine where they were born. This may sound like pagan wizardry to the inexperienced, but it's a scientific technique called "isotope ratio mass spectrometry." Middle West.
Despite this new data, "we don't know how or why they're getting to Florida," said Vander Zanden.
Why would a small band of monarchs, some from the east coast and maybe some from the Midwest, choose Florida over Mexico? Scientists have been speculating about this for at least four decades.
Fred Urquhart, co-discoverer of the monarchical winter colonies in the 1970s, called monarchs who traveled to Florida "aberrant" and lost the attempt to find Mexico. Another pioneering monarchist, Lincoln Brower, argued instead that the monarchs intended to come to Florida. "And we still don't have an answer to this day," said Davis.
Jaret Daniels, curator of Lepidoptera at the University of Florida Museum.
One reason: there isn't a lot of historical data.
Ray Moranz is a pollinator ecologist with the nonprofit Xerces Society for Insect Protection. He studied with Lincoln Brower at the University of Florida in the 1990s. "Twenty or thirty years ago," said Moranz, "people just thought, 'Monarchs are on their way to Mexico, why should they be tagged in Florida?' And now we have almost no idea how many came here earlier."
For decades, however, scientists have observed a large annual migration of monarchs east of Tallahassee and southwards, at a time when the rest of the population is reaching Mexico. The Atlantic coast is probably a normal hiking route for beach-loving hikers. Perhaps they don't have much of a choice: New England monarchs could be wedged between the Appalachians and the sea and headed to Florida.
As for the wandering monarchs of the Midwest, "We still don't know if they're going to take the wrong turn on their way to Mexico," said U-Madison's Oberhauser.
"There were never enough people marking tags in Florida," said Moranz of the Xerces Society. "And it's still not enough."
Scientists have indicated that in the near future, there will be an impressive crop of new monarchal studies that are slowly starting to fit the Sunshine State better into the bigger picture.
In the end, Florida can matter
Since monarchs were only on the waiting list for the Endangered Species Act last year, understanding their decline only wins national attention. That also makes it more important to solve some of the mysteries that surround the long-ignored Florida people.
With the North American monarch population declining by over 80% over the past few decades, including visits to Florida may be important to the species' overall recovery. As long as it doesn't parasite them or keep them from migrating.
Fred and Norah Urquhart, who first discovered the migration destination of the monarchs in Mexico in the 1970s. Fred Urquhart said monarchs traveling to Florida were lost on a "deviating" route.
Fortunately, there is an easy solution for those who have already planted tropical milkweed: just prune it back or bring it indoors in winter. "I, too, grow tropical milkweed just because it's simple and beautiful," said Anurag Agrawal, Cornell University professor of environmental studies who specializes in the relationship between monarchs and milkweed, on his website last year. “Just adding [tropical milkweed] at the end of the season is probably fine. Even so, I always worry when people advertise planting lots of it to help the butterflies. From a nature conservation perspective, I simply recommend general habitat protection and the planting of native species. "
For those who hold onto their tropical milkweed cannons, Daniels at UF recommends growing them from seeds or cuttings, as the commercially sold plants are often contaminated with deadly pesticides.
"We're not saying you are not helping [the Florida monarchs]," said UGA's Davis. “We're just saying that we help them differently. Native planting is something that the entire state of Florida must do together. "
For more information on tropical milkweed and native species, contact the Xerces Society and the University of Florida. You can also read why Tallahassee Native Nurseries has stopped selling the non-native plant.
Krishna Sharma, who recently earned a Masters in Ecology from the University of Georgia, reports for The Herald as a Mass Media Fellow of the American Association for the Advancement of Science (AAAS).
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