The Illinois Department of Agriculture says two more counties have been put under quarantine because of emerald ash borer infestations.

Infestations have been confirmed in Henry and Knox counties, and they'll join 39 other counties under quarantine because of the destructive beetle.

The larvae of the small, metallic-green beetle burrow into the bark of ash trees, causing the trees to starve and eventually die.

The bug is native to Asia and was discovered in Michigan 10 years ago. Since then, it has killed more than 25 million ash trees.

Signs of infestation include thinning and yellowing leaves, D-shaped holes in the bark and new shoots growing from the bottoms of tree trunks.

The quarantine forbids the movement of live ash trees or their wood products outside of the quarantine area.