"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."