When supposedly good bugs go bad

updated 11:18 a.m. ET July 23, 2009

SAN FRANCISCO - Imported insects have been deployed as foot soldiers in the fight against invasive bugs and plants that cause billions of dollars in damage each year. But some of those imports are proving to be pests themselves that upset the balance of nature and threaten native species.

A weevil released to attack a weed has veered off target and is gobbling up a native plant in Nebraska. A fly that was supposed to kill invasive moths is wiping out native moths in New England. And an insect introduced to combat a pesky weed led to a spike in the population of mice carrying a potentially deadly virus in Montana.

Despite such scattered scientific mishaps, the Associated Press found the federal agency that has approved the importation and release of hundreds of insects over the past three decades seldom tracks their effects on other species and the environment and does not even know whether most of the introduced bugs have died off or thrived unchecked.

It largely leaves the monitoring of bug releases to states and researchers who critics say have little funding or inclination to track impacts that might not show up for decades.

Too many insects have been let loose without understanding their effectiveness and the long-term consequences, critics say. Although only a relative handful of biological controls are known to have gone wild, they say there is potential for unpredictable harm from others.

"If you find you've got a problem with a chemical, you can stop spraying it," said Daniel Simberloff, an environmental science professor at the University of Tennessee, Knoxville. "If you find you made a mistake with a biocontrol agent, you can't call it back."

The mongoose fiasco
In one of the most infamous disasters, farmers introduced the mongoose to Hawaii in the late 1800s to control rats that were feeding on sugar cane. Rather than control rats, the mongoose have preyed on the nests of endangered and threatened native birds.

In the past decade, researchers found that a parasitic fly, released as late as 1986 to combat gypsy and brown tail moths, is devastating the native silk moth population in New England.

INTERACTIVE Alien invaders Interlopers threaten native species

But supporters view biological controls as an alternative to widespread pesticide and herbicide use, and say the science has come a long way.

Scientists now spend years vetting critters to make sure they do not feed on what they are not supposed to, said Mark Hoddle, an entomologist with the University of California, Riverside.

Despite some recent lapses, advocates of biocontrol point to successes.

The vidalia beetle from Australia in the late 19th century helped save California's citrus industry, which was ravaged by a scale insect, Hoddle said. In the 1940s, Klamathweed beetle helped control St. John's wort, a weed that is toxic to livestock and crowds out native plant species.

"The alternatives are do nothing, let (the invasive species) do what it does, and suffer the consequences," Hoddle said. "Or spray insecticide or herbicide like crazy. That's expensive, pollutes the air and contaminates our groundwater."

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