It's Invaders vs. Invaders as Scientists Target Alien Species

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The insects were released between 1999 and 2003 and have slowed bridal creeper's spread.

In 2000 the Australian government approved release of the rust fungus Puccinia myrsiphylli. The fungus infects the leaves and stems of the bridal creeper, diverting resources the plant needs for growth and reproduction.

Later, in 2002, the bridal creeper leaf beetle was released. The beetles' larval young strip the shoots and leaves that enable the plant to climb, which prevents it from reproducing and spreading to new areas.

According to Scott, more than a thousand community groups in Australia are involved in release programs, helping to spread bridal creeper's enemies and to curb the invasive weed's progress.

U.S. Invasion

The U.S. is also serious about controlling invasive weeds, said Cressida Silvers, an entomologist with the U.S. Department of Agriculture's Agricultural Research Service (ARS) in Fort Lauderdale, Florida.

She and her colleagues go to Australia in search of enemies of melaleuca, an evergreen tree native to Australia but considered an invasive weed in the U.S.

The tree was introduced to the U.S about a hundred years ago and now infests over 500,000 acres (200,000 hectares) of the Florida Everglades.

Melaleuca trees, whose seeds are spread by fire, are fast growing and clump together, crowding out native vegetation and sucking wetlands dry.

Melaleucas spread at an average of 15 acres (6 hectares) per day, according to ARS research.

After about a decade of study, scientists introduced the melaleuca weevil to the Everglades in 1997. This short-snouted insect munches the trees' young leaves.

The weevil stunts melaleuca growth, increases the mortality of young trees, and reduces flowering and seed production.

In 2002 the government scientists released the melaleuca psyllid, a sap-sucking insect that has the same effect as the weevil.

"We consider them a tremendous success," Silvers said. In one study area, for example, 65 percent of young trees fed on by the enemy insects died.

But ARS researchers stress that herbicides and physical removal of invasive species are also important weapons in the ongoing battle.

Biocontrols "are not a replacement, but a good tool to go along with the other good tools we have," Silvers said.

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