Insect army deployed to fight invasive Brazilian pepper trees in the Everglades

A thousand teeny troops fanned out Tuesday. Their mission: Take down an invading green horde.

At the deployment, scientists opened 100 vials, each containing 10 lab-raised bugs called thrips, freeing them into new pastures: a Brazilian pepper-infested Broward County park.

The liberation happened before an audience of journalists and officials, to demonstrate how subsequent releases into the Everglades will work.

Knocking back invasive pest plants is key to restoring the River of Grass, said South Florida Water Management District scientist LeRoy Rodgers, who’s worked on the biocontrol project more than a decade.

Though controlling flow and pollution is often top-of-mind in Everglades restoration, Rodgers points out that healing the landscape is crucial as well.

“We know that getting the water right is critical, but if we also don’t take care of these invasive species, are we really going to have a restored Florida Everglades?” Rodgers, section leader for the district’s invasive species unit, asked.

Soft-bodied sap-suckers, these thrips – their scientific name is Pseudophilothrips ichini — feast on the tender growing tips of the peppers. Only a few millimeters, they're about half as long as a grain of white rice. Gardeners may be familiar with other thrips varieties, which ruin rose buds and other ornamentals.

Not only do thrips stunt the peppers’ growth, “it can cause the flowers to abort,” Rodgers said. No flowers means no seeds, and “anything we can do to reduce flowering will help take the edge off this invader.”

A scourge to Florida’s wilderness areas for more than a century, Brazilian peppers originally were imported as landscape accents. But the poison ivy relatives escaped into the wild, creating dense thickets where little else can grow. 

“Even a bunny rabbit couldn’t find anything to eat, it gets so thick and dark in there,” said Gene McAvoy, Hendry County Extension Service director. “Brazilian pepper is a huge problem – I have just a small ranch, and I have to spend five or six weekends a year dealing with it.”

Multiply that across the Everglades, and you have a massive, expensive ecological mess, he said. What’s more, Brazilian pepper hosts another troublesome invader, a root weevil that bedevils the state’s citrus crop, McAvoy said.

In south and central Florida alone, scientists estimate 1,093 square miles are pepper-covered. By way of comparison, Lee County is 804 square miles. Controlling them costs land managers millions of dollars. On district land alone, “It costs more than $1 million each year to control Brazilian pepper with mechanical and herbicide (means), so over the long term, we’re talking tens and tens of millions of dollars,” Rodgers said.

Enter the thrips.

The hope is they will be as successful as several other exotic-eating critters, like the air potato beetle and the melaleuca sawfly, both of which have made significant dents in the invasive plants.

To those concerned about unintended ecological consequences, Rodgers points to the time and pains taken with the $5.5 million project, a partnership between the district, the Florida Fish and Wildlife Conservation Commission and the U.S. Department of Agriculture, the U.S. Army Corps of Engineers, the Florida Department of Environmental Protection, the National Park Service and the University of Florida Institute of Food and Agricultural Sciences.

“We have to be very careful in the process of introducing an insect from another part of the world here. The last thing we want is an insect used for biocontrol to become yet another invasive species problem in Florida. For that reason, we’ve done a great deal of research to show that this insect will not feed on any other plants besides Brazilian pepper, nor will it cause … any irritation to humans or livestock.”

McAvoy rates the possibility of disaster as “infinitesimal.”

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The project started with entomologists heading to South America, where Brazilian pepper is native, to hunt for the tree’s natural predators. Once they found insects that eat the peppers, they tried to identify insects that feed on them exclusively.

“We do initial tests where we introduce the insect to very closely related species (because) some insects that are generalists,” Rodgers said, “that maybe will also eat on a mangrove tree or whatever. So over there, we introduce the insect to a number of other plants, and as soon as that insect feeds on another plant, we disregard that insect and move on.”

The critical hurdle is what’s called a starvation test. Only insects that prefer to starve rather than eat a plant other than Brazilian pepper pass.

“We have to make sure the insect won’t feed on another plant,” he said. So far, all of the research has happened in quarantine but now, Rodgers said, “we’re entering into a new phase where the federal government has given a permit to allow for the release of this insect in Florida."  The next phase is to see how it establishes.

Though he’s optimistic, Rodgers acknowledges it may not work.

“We’ve had a long history of biological control for other weed pests and it’s not always 100 percent. Sometimes these insects do great, and sometimes they fizzle out,” he said. “We’re certainly hopeful they’re going to persist and spread across the landscape.”

Because thrips crawl for most of their life cycle and only fly short distances as adults, they don’t travel fast and will have to be taken to restoration sites.

“We already know they’re not going to spread themselves rapidly, (so) we will be doing a lot of releases across the landscape,” Rodgers said. “It’s not like we can just release them in one location and they will just spread like doves.”

In the future, if funding and approval materializes, Rodgers said, they may be made available to landowners, as air potato beetles are.

For now, the insects only will be used as part of the Comprehensive Everglades Restoration Project’s biocontrol program. Going forward, the U.S. Army Corps of Engineers will partner with the district to spend about $300,000 annually to raise and release the thrips.

“The more we can get these insects out there doing their work on their own," Rodgers said, "the less we have to rely on other methods like costly mechanical control.”

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