Invasive bugs and plants cause billions of dollars in damage every year.  Instead of using chemical pesticides, researchers have turned to imported insects to fight them.  But some of the outsiders are upsetting the balance of nature and threatening other species. 
According to the Associated Press, an agency that regulates the release of hundreds of insect agents doesn't track what happens to them, or potential bad effects on the environmen.
As a professor at the University of Tennessee warns, "If you've got a problem with a chemical, you can stop spraying it.  If you make a mistake with a biocontrol agent, you can't call it back."