Moth may be the secret to curbing fern’s growth

MIAMI — Compared to kudzu, the infamous vine that ate The South, Old World climbing fern may be an obscure pest plant. But they’re a lot alike.

The fern just has a slightly smaller appetite. It’s only eating South Florida.

It’s been doing it at an alarming pace, smothering more than 130,000 acres from cypress forests to Everglades tree islands to coastal mangroves in dense cloaks of death — despite millions spent trying to halt it with sprays, spades and machetes.

But a new weapon — in development for a dozen years by federal researchers in Fort Lauderdale — shows significant promise to beat back an invader so aggressive it would cover a third of the wetlands between Orlando and Naples if left unchecked.

It’s a nondescript moth, a “bio-control” dubbed “Neo,” a nickname considerably catchier than Neomusotima conspurcatalis.

Discovered near Hong Kong in 1997 by Bob Pemberton, an entomologist with the U.S. Agricultural Research Service, Neo has produced millions of hungry larvae that have chewed through thick fern blankets with stunning gusto in three field tests.

“I have never, in all my career, seen a biological control that looks as promising as this one,” said Dan Thayer, who directs invasive-plant control for the South Florida Water Management District.

“My jaw dropped,” he said, when he saw how Neo colonies in Jonathan Dickinson State Park in Martin County stripped ferns naked.

Though they stress it’s still early, Pemberton and fellow entomologist Anthony Boughton, both based at the U.S. Department of Agriculture’s Invasive Plant Research Laboratory in Fort Lauderdale, agree Neo is a ray of hope for what seemed an almost impossible task: stopping an exotic fern, formally known as Lygodium microphyllium, considered among the most serious threats to the Everglades.

“The Lygodium is strangling the Everglades in a more profound way than Burmese python would ever be able to do,” said Pemberton.

“The difference is Lygodium completely transforms the environment. It turns healthy native populations into completely artificial, greatly diminished environments.”

Much like kudzu, the fern can trellis up trees 90 feet high. The mat, up to a yard thick, blots sunlight and slowly kills everything beneath them.

Though found mostly in small scattered patches back home in tropical Africa, Asia and Australia, it has exploded in South Florida.

Cold weather likely limits any march north of Orlando, but with nothing that eats it here, it has spread west and south since being found in Martin County in the 1960s. The pace picked up exponentially in the 1990s.

Loxahatchee National Wildlife Refuge alone, Pemberton said, spent some $5 million last year on aerial spraying to try to rescue enveloped tree islands. So far, the fern is less established in Everglades National Park but has infested 10,000 acres of mangroves on the southwest coast.

Thayer puts the fern at No. 1 on Florida’s most unwanted plant list. It also ranks among the most difficult and expensive to combat. Herbicides can knock it back but are costly and hard to safely apply in wetlands. Killing it requires labor-intensive root cutting and removal.

Fire, normally a natural exotic control in the Glades, can snuff it. But the thick ferns also carry flames high into the canopy, killing native trees that would normally survive.

“I’d say it was worse than kudzu,” said Thayer.

The district is among a number of state and federal agencies that have helped bankroll the USDA search for a bio-control — meaning something from back home that feeds on it.

Information about the fern was so scant when Pemberton began his search that he had no idea what, if any, candidates he might find. Just locating plants can be a challenge, he said. “In the native range, these weeds that are dominant here are often uncommon.”

He found Neo larvae munching a patch outside of Hong Kong and the little moth joined a few dozen possibilities.

Though Florida has a long history of misguided imports — melaleuca to drain the Everglades, for instance, and blue tilapia to clear weeds in canals — the screening is far more rigorous nowadays. The USDA process takes years.

Counterparts in Australia first ran Neo, and other bugs, through tests to ensure its appetite was isolated to the fern. In 2001, it was brought to a USDA lab in Gainesville to breed a population for more testing and, after environmental and biological assessments and approvals from more than 20 state and federal agencies, Pemberton and Boughton released Neo in January 2008 in Jonathan Dickinson.

They weren’t particularly optimistic — in part because it was actually choice No. 2. Another moth, easier to find and common in Australia along the same latitude as South Florida, went first in 2005 but did not take.

Lab testing, Pemberton said, can pinpoint insect diets but is far less successful predicting how species will do in the wild. In the first months, Neo also looked nil.

“We were actually having some difficulty in relocating the insects in some of the locations,” Boughton said.

By summer, though, Neo heated up. At one point, Pemberton said, moths were “flying like snowflakes” among the cypress.

Boughton, charged with tallying population, had no problem. Larvae were thick — 600 to 800 caterpillars per square meter — and they left squiggly telltale trails of “frass,” as in frass happens.

“They’re little sausage makers,” Boughton said. Fern in, frass out. Like that.

In a soon-to-be-published research paper, the scientists reported Neo numbers rocketing from 31,091 releases to 1.6 million to 8.2 million larvae at site.

Neo had stripped some 3.5 acres of fern and expanded its range, moving to adjacent areas a third of a mile away.

Now, researchers are working with state and federal park and land managers to expand releases, starting in fern-choked Loxahatchee.