Advertisement
  1. Archive

Prickly problem

An exotic moth with a taste for a rare cactus found in the Florida Keys feasts its way north.

If you've got a prickly pear growing in your yard, Peter Stiling wants you to go look at it right now. See if the normally solid cactus pads seem translucent, as if they're being eaten from the inside out. See if the cactus looks like it's about to collapse.

If so, he wants to hear from you.

For most of this decade Stiling, a University of South Florida professor, has been tracking an exotic moth that killed a very rare cactus in the Florida Keys and since then has been discovered feasting on more common cacti in Pinellas, Hillsborough, Duval and Brevard counties.

"I'm very keen to know how far it's spread in Florida," he said.

The fear among biologists is that the moth _ Cactoblastis, more commonly called the cactus moth _ will cross the Gulf Coast and get into Texas, then start wiping out thousands of acres of cacti in the deserts of the Southwest.

To see what the moth can do, Stiling says, take a look at Australia, where it is regarded as a hero.

Exotic cacti were introduced into Australia in the early 1800s. By the 1920s they had spread across 58-million acres, covering about half of it so densely that the land became useless for agriculture.

So in 1925, Aussie authorities imported about 3,000 cactus moth eggs from the moth's native Argentina. By 1933, the moth's voracious caterpillars had virtually rid the range of prickly pears. Grateful ranchers built a Cactoblastis Hall that still stands today, the only building dedicated to fond memories of an insect.

In the 1950s, landowners in the Caribbean decided they, too, needed to clear some pesky native cacti off their property, Stiling said. They brought in the cactus moth, and it did its job. But then the cactus moth began jumping from island to island.

In 1989, a researcher found it on cacti in Cuba. Curious, he called Fairchild Tropical Garden in Miami to ask if the moth had turned up in Florida. At first the answer was no.

A year later, though, there it was in the Lower Keys, munching on the semaphore cactus. At that point, there were only 12 semaphore cacti left in the wild in the United States, making it one of the rarest plants in the country and perhaps the world.

Until the moth showed up, the semaphore seemed to have at least a fair chance of avoiding extinction because its last colony stood on land owned by the Nature Conservancy.

Yet before Nature Conservancy officials could stop them, cactus moth caterpillars killed one of the semaphores in 1991, said Chris Bergh, the conservancy's South Florida land steward.

Conservancy officials contacted Stiling, an expert on insect ecology, and he has been helping them try to battle the cactus moth ever since.

It has been a frustrating experience.

"I used to think, in my naivete, that it would be easy to save a species," he said.

Not until early last year did he realize how tough a job it would be. Yet who could have predicted that some of America's rarest plants would be killed by one of America's rarest animals?

Poachers and little hooves

The mature semaphore cactus looks like a signalman waving flags. The message is probably, "SOS."

First identified by a biologist in 1919, the semaphore once grew thick throughout the Lower Keys. But over the years, man's need for land to develop whittled away the semaphore's habitat until only a dozen remained, said Doria Gordon, state ecologist for the Florida chapter of the Nature Conservancy.

Poachers have taken their toll too, Gordon said. When the conservancy bought its land, there were knife and machete marks on the trunks where collectors had chopped off parts to try to grow some of the rare plants at home. Conservancy officials are now loath to identify exactly where the last colony grows.

Experts at Fairchild and USF's Botanical Garden have succeeded in growing semaphores in greenhouses. But when they have tried transplanting them back into the coastal hammock where the wild ones grow, the young cacti usually fail to reach adulthood.

Then along came the cactus moth, complicating things further. It lays its eggs in an egg stick that so closely resembles one of the cactus' own spines that it is hard to spot. Then, when the moth's larvae are born, the little red and black caterpillars burrow into the cactus where pesticide cannot reach them.

Because the moths have attacked a lot of different cacti, it is almost impossible to wipe them out.

They have been found munching on common prickly pears at Fort De Soto Park in Pinellas County and Upper Tampa Bay Park in Hillsborough County, Stiling said. And on a key near where the semaphores live, they have badly infested a stand of exotic Indian fig cactus "as big as a bus," he said.

The conservancy is working with the landowner to remove the entire stand and incinerate it, just to protect the semaphores, Bergh said.

When conservancy officials find a semaphore cactus that's being chewed up by Cactoblastis, they cut out that pad, like surgeons cutting out an infection before it can spread. As for the caterpillars, Gordon said, "stepping on them is good enough."

Conservancy officials decided to protect the semaphores by putting cages over them. The adults got big cages, built out of 4 by 4s and window screens. The little ones were covered with smaller cages of mosquito netting.

The cages created new problems. In addition to keeping out moths, they also kept out the birds that spread the plant's pollen, preventing the natural propagation of the species.

But the worst problem was caused by the diminutive Key deer from nearby Big Pine Key. The white-tailed deer, about 3 feet tall, are among the rarest American mammals, with a population estimated in the range of 250 to 350.

When the little deer saw the little cages, Stiling said, they decided it was the perfect place to rub their antlers. The rubbing led to trampling of the cacti.

The little hooves also trampled Stiling's optimism. It taught him that good intentions and scientific expertise might not be enough to save a species.

"When I saw that, I had a change of heart," Stiling said. "You try and solve one problem and you end up creating a new one. . . . We're on top of it, we're doing all we can, and they're still going to wink out."

Like unpouring water

As Hurricane Georges barreled toward the Florida Keys last year, conservancy officials decided to uncage the semaphores. Moths had not bothered the semaphores for a while, Gordon said, and the storm might turn the cages into battering rams.

Sure enough, the hurricane killed one of the semaphores. There are now only 10 adults left.

The cages were expensive to build, and the conservancy was unable to afford new ones, Gordon said. So the conservancy left the semaphores uncaged, instead depending on a cadre of volunteers to closely inspect the semaphores once a week, looking for the hard-to-spot egg sticks.

They missed one.

Two weeks ago, Stiling and Bergh were checking the semaphores and spotted the telltale signs of infestation. Bergh cut it out of the cactus and destroyed the larvae.

"I hope we nipped it in the bud," Bergh said.

Ultimately, conservancy officials will try to raise enough money to build new cages, Gordon said. Until then, Bergh said, the volunteers are patrolling the semaphores twice as often. Meanwhile, the moth may be moving north.

"The threat is enormous," Gordon said, "'and we don't even have an approach to dealing with it yet."

Stiling said there has been talk of bringing in a wasp that lays eggs in the larvae, killing them. But that may lead to a need to try to control the wasp, he said. It becomes like the children's story of the old woman who swallowed a fly, he said.

"Once you release something like this into nature, what are your chances of ever controlling it again?" Stiling asked. He compared it to unpouring a pitcher of water.

Despite all the problems that have plagued the efforts to save the semaphore, Stiling said, he still believes there is a chance to keep the species from disappearing from the wild.

"I would like to think the chances of saving the semaphore cactus are better than 50-50," Stiling said. "But the odds of stopping the Cactoblastis, I'd say, are close to zero."

_ Times researcher Kitty Bennett contributed to this story.

Handling the pest

If you see the red-and-black caterpillars of a cactus moth on a prickly pear, or see an egg stick, contact Peter Stiling at the University of South Florida at (813) 974-3754, or e-mail him at pstilingaol.com

YOU MIGHT ALSO LIKE

Advertisement
Advertisement