Grasshoppers Used to Fight "Worst Water Weed"

April 1, 2003

Researchers are counting on a small South American grasshopper—Cornops aquaticum—to help them combat the "world's worst water weed": the water hyacinth, which chokes waterways in Asia, Africa, Australia, and the Americas.

Away from its native habitat on the upper Amazon basin, the water hyacinth grows fast and spreads furiously, causing woes for man and beast. Cornops is the latest weapon in what researchers call "biocontrol"—pitting one kind of creature against another. But such methods sometimes cause environmental problems.

"Ideally I would like a magic bullet—one insect that will do 100 percent of the job," said Ted Center, an entomologist and research leader at the Invasive Plant Research Laboratory in Fort Lauderdale, Florida, who is known as "Mr. Waterhyacinth" because he has studied the plant for more than three decades.

But "each introduction has an element of risk," he said, "and the more insects we release the higher the chance of unanticipated results. We need to fit biocontrol to local needs."

Dark green with dazzling purple-blue blooms, the water hyacinth floats on lakes, streams, ponds and rivers. Doubling in size every 7 to 12 days, it can grow up to six feet (1.8 meters) tall and trail three-foot-long (0.9-meter-long) roots.

"The water hyacinth has affected just about every lake, river, and dam in sub-Saharan Africa," said Martin Hill, an entomologist at Rhodes University in Grahamstown, South Africa. "It hinders the extraction of water for industrial, agricultural and domestic purposes. In rural areas it can completely block access to water."

Worldwide Menace

Floating islands of the plants also become breeding grounds for mosquitoes and snails that respectively cause malaria and schistosomiasis.

The water hyacinth invaded the United States during the 19th century.

"The first mention of the plant was in 1884 at an international cotton exposition in New Orleans, where it was given away as a souvenir," said Center.

By the 1890s water hyacinth already occupied the southeast coast of the U.S., infesting Florida, Texas, South Carolina, and Louisiana, which still has the biggest problem.

For decades man has fought the pest with an arsenal of more-or-less costly methods. Mechanical harvesters—a tugboat-mower—are slow. Herbicides are a quick fix, though with dangerous side effects.

Continued on Next Page >>




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