Die, Weed, Die!

An alien moth munches an invasive fern into extinction

The saw grass crackles as the party of scientists wends its way through the serrated blades. A red-tinged bird chatters angrily at the intruders. The ten-foot perimeter of saw grass gives way to muckier ground with waist-high shrubs. If cave explorers go spelunking, then Everglades surveyors must go spelooshing, because that's the sound of extricating one's foot from the muddy soup.

The interior of the island is cordoned off with a thick wall of willows, vines, and holly. The plan is to use a compass and walk a straight east-west line across the island, keeping one eye out for Old World fern and the other on things like a ubiquitous prickly concertina wirelike vine that would sooner decapitate visitors than allow them passage. Furedi and her research team of three or four will spend four or five days a week trekking through tree islands like this.

One bio-indicator for Old World fern appears to be "moss collars." These grow at the base of trees and as high as four feet from the ground. So when the four researchers chance upon a decomposing log with a crewcut of green moss upon it, they crouch down under the dusky canopy. There they spy minuscule sporelings in the first stage of spore growth. Furedi takes a small plastic container from her backpack and inserts a chunk of moss-laden wood. It's the closest thing they'll see to Old World fern today.

Owen Richardson
The caterpillars of this moth, the Austromusotima camptonozal, eat 
Old World fern. It's the first insect released against the dreaded plant -- 
but not the last
Christine A. Bennett
The caterpillars of this moth, the Austromusotima camptonozal, eat Old World fern. It's the first insect released against the dreaded plant -- but not the last

Back in the research lab, Volin will grow the sporelings. He's conducting the same experiment in Australia, using that country's different soils. In the end, he hopes to learn if the soil has some effect on their life cycle.

So far the news is not good. This is one malleable plant. The fern is something of a sex addict, having evolved as a bisexual that can germinate its spores in any of three ways possible for ferns. The first spore to germinate in a new area is almost always female, researchers found, which then produces a pheromone that transforms surrounding spores into males.

Most ferns are very particular about moisture levels during germination; this fern has a more "whatever" attitude. It's not picky about light either; it can grow in dark shadows or in full sunlight atop trees. "This is an incredible plant," Volin enthuses. "The question is: Why is it not invasive in its own native area?" he poses. "We don't know that."

In the coming few years, the battle against Old World fern will be mostly waged with conventional weapons: herbicides, pruning shears, and elbow grease. But at the front line, soldiers know ultimate victory calls for greater weapons than those.

"The best hope we have is biocontrol," says Melvin, who stands at the edge of the moth-populated tree island. A wall of thick ferns dwarfs her. There's no sign of the fern-eating moths today, but it's a big island, and the tiny insects can't have made much headway yet. Who really knows how well these winged warriors will do in the war against Old World fern?

They're a long way from home, and their enemy is so very well entrenched. And reproducing fast.

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