Environmental Valuation & Cost-Benefit News

Link: http://www.sptimes.com/2005/09/27/Citrus/A_battle_left_to_a_be.shtml

Julio Medal and Vince Morris grew more excited with every step they took toward a patch of eerily vibrant shrubs growing among the pines in the Withlacoochee State Forest.

From a distance they could see a few of the bushes had turned a dull green; up closer they noticed "shot holes" gnawed in the leaves.

Closer still - and this really thrilled them - they saw a tiny green bug partly hidden by a clump on its back.

"Dung umbrella," Medal, a University of Florida entomologist, said with satisfaction.

"That's a great sign," said Morris, an ecologist with the state Division of Forestry. "That means they are being born here."

"They" are gratiana Boliviana , a South American insect for which Medal has come up with another, more descriptive name: tropical soda apple leaf beetle.

This bug with its own unusual defense - carrying a bundle of its dung in the larval stage to discourage predators - is the best long-term hope to breach the defenses of the soda apple, one of the most destructive of the legion of invasive plants in Florida.

Soda apples, originally from South America, first appeared in Florida in 1988, Medal said. Unchecked by natural enemies, the plant has advanced to over 1-million acres in Florida and into several other states in the Southeast.

The prickles covering the plant's leaves and stalks prevent the grazing that might otherwise help control it.

The fruit, unlike the leaves, is favored by a variety of animals, including birds, raccoons, coyotes and cows, which distribute the seeds in their manure as they wander over pastures.

So, more than any other invasive plant in the state, soda apple is not just an environmental threat, but an economic one, Morris said.

Beyond the loss of productivity as the plant consumes pastures is the expense of controlling soda apple with a repeated combination of mowing and spraying, which costs about $30 per acre.

Also, ranchers in Florida must frequently quarantine cattle before shipping them to other states.

"It's a suggested holding period to give those animals a chance to clear any seed from their digestive track," said Ed Jennings, the regional agricultural extension agent who specializes in livestock.

While biological control has become common in the fight against exotics, the targets usually threaten only the natural system.

In the battle against the soda apple, researchers are fighting to protect a major industry "It seems like when something hits a big economic interest, like the cattle industry, we find the resources to battle them," Morris said.

The U.S. Department of Agriculture has contributed hundreds of thousands of dollars to Medal's research, which began with his identification of the leaf beetle in Brazil in 1994.

It was not until 2003 that he was able to release the first batch of 3,000 bugs; he expects to turn loose 100,000 this year in 18 counties - including Pasco, Sumter and Hillsborough - and 100,000 next year.

The long delay is due to the pains taken to avoid some of the previous disasters of biological control. In many cases, animals brought in to fight an exotic pest have become pests themselves, with examples including the grass carp in Florida.

The release of the leaf beetle is particularly tricky because insects that like to eat one plant are often tempted by its closest relatives, Medal said.

And the soda apple's family includes some of the most valuable crops in the world, including peppers, eggplants and tomatoes.

All had to be tested - meaning researchers had to give the beetle a chance to eat them and make sure they declined. Fortunately, Medal said, the leaf beetle turned out to be so picky it even turned away from another, nearly identical soda apple with red fruit rather than yellow.

Releasing the beetles is as low-tech as a grade-school science project.

On a recent morning, Medal and Morris drove to the first of two sites infested with soda apple in the Withlacoochee State Forest. The site was formerly the grazing grounds of another exotic - the state's herd of cracker cattle, descended from cows imported by Spanish conquistadors.

These cattle, presumably, ate hay contaminated with soda apple seeds and then deposited them under the pines, where the soda apple plants now grow as vigorously as azaleas in Augusta, Ga.

Morris opened one of two large, ventilated plastic jars that Medal had brought down from his Gainesville lab. Inside, about 100 beetles crawled over wilted soda apple leaves.

Morris draped the bugs over the tops of the plants and then unceremoniously dumped out the few insects that clung to the bottom of the container.

Much more dramatic is the damage 300 beetles have done since their release a month earlier.

Targeted plants showed some signs of distress - perforated, limp leaves as well as a few defoliated branches. The beetles, meanwhile, are thriving and regenerating, Medal said.

That means Medal's project is on its way to success. He foresees releasing bugs throughout the state over the next few years. Eventually the beetle will occupy the same place in Florida's natural system that it does in South America - not eliminating the soda apple, but containing it.

By DAN DeWITT
St. Petersburg Times www.sptimes.com
http://www.sptimes.com/2005/09/27/Citrus/A_battle_left_to_a_be.shtml