A tree-killing beetle has been discovered in northwestern Illinois' Jo Daviess County.

The Illinois Department of Agriculture says the discovery of the emerald ash borer means the beetle has invaded the entire northern one-third of the state.

The small, metallic green bug is native to Asia. It was discovered in Michigan in 2002, where officials suspect it arrived in wooden packing crates.

Since then, it has spread to surrounding states and killed tens of millions of ash trees.

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The beetles' larvae burrow under the bark of ash trees, eventually starving them to death. Signs of infestation include yellowing leaves, D-shaped holes in the bark and new shoots near the base of the trunk.

Officials say there probably still is time for Jo Daviess homeowners to treat their ash trees.

I'm the city editor at the Quad-City Times. You can reach me at dbowerman@qctimes.com or 563-383-2450.