The tree-killing emerald ash borer is continuing its march through Illinois and has reached the southern part of the state.
The Illinois Department of Agriculture said Friday the small, metallic-green beetle native to Asia has surfaced near Salem in Marion County and at an Interstate 57 rest area in Effingham County.
The beetle now has been confirmed in 20 Illinois counties.
Agriculture experts say its larvae feed on the inner bark of ash trees, disrupting the flow of water and nutrients. But the insect doesn't pose any direct risk to public health.
The supervisor of the state's effort to stop the spread of the beetle says detections are increasingly occurring along major highways or near key intersections. That suggests the beetle may be using transportation corridors to proliferate.