Experts have decided to battle the invasive emerald ash borer with a natural predator.
About 1,000 wasps were released into a Lake County forest preserve on Thursday in another effort to stop or slow the spread of the beetle, which is native to Asia.
The imported wasps, which are less than half a centimeter long, are native to China and feast on ash borer larva.
John Lelito, who heads the Michigan lab that raises the wasps, says two species of wasps that attack the beetle are being deployed in Lake County.
The wasps were released in Cook County forest preserves in 2009, where officials say they have had limited success in controlling the beetle.
The larvae of the metallic-green beetle feed on the inner bark of ash trees, killing them.