State officials have expanded a quarantine in northern Virginia to prevent the spread of a tree-killing beetle.

A quarantine was issued in Fairfax County after the emerald ash borer was found at two sites there earlier this month.

The metallic green beetle feeds on the layer of wood just beneath the bark of the ash tree, cutting off water and nutrients.

On Tuesday, the Virginia Department of Agriculture and Consumer Services added Arlington, Fauquier, Loudoun and Prince William counties to the quarantine, as well as the cities of Alexandria, Fairfax City, Falls Church, Manassas and Manassas Park.

The order prohibits the movement of ash trees, untreated ash lumber products and hardwood firewood outside of the quarantined area.

Since its discovery in 2002, the beetle has spread to Maryland, West Virginia and Virginia, among other states.