State Department of Agriculture officials say the destructive emerald ash borer has been found in Lee and Henry counties in northern Illinois.

The borer is a small, metallic-green beetle whose larvae burrow into the bark of ash trees, eventually starving the trees to death.

Signs of infestation include thinning and yellowing leaves and D-shaped holes in the tree bark.

The beetle is native to Asia and is believed to have arrived in the Midwest about 10 years ago via wooden shipping pallets. It's since killed more than 25 million ash trees.

The recent discoveries bring the number of Illinois counties with confirmed infestations to 26 - more than one-fourth of the state. Thirty-nine counties are under quarantine to prevent people from spreading the beetle by moving wood products.