Emerald ash borer beetles, an insect that can destroy an ash tree within three years of the initial infestation, have been found in Allegheny Township, Pennsylvania Department of Agriculture Secretary Dennis Wolff said today.

The beetle was first detected in Butler County in 2007, and then found in Allegheny, Beaver, Lawrence, Mercer, Mifflin, and now, Westmoreland County.

All seven counties are under a quarantine to restrict the movement of ash nursery stock, green lumber and other ash material including logs, stumps, roots, branches and wood chips, according to a news release from the Pennsylvania Department of Agriculture.

All types of hardwood firewood species, including ash, oak, maple and hickory, are quarantined, since it is difficult to distinguish between species. Campers and homeowners are advised to use only locally harvested firewood, to burn the wood on-site and to not carry it to new locations.

The emerald ash borer, native to China and eastern Asia, probably arrived in North America in wood packing materials. The beetle species was first found in southeastern Michigan and Windsor, Canada, in July 2002, and since then, the beetles have caused the death and decline of more than 20 million ash trees in Michigan, Indiana, Maryland, Virginia and Illinois, according to the news release.

The beetles leave D-shaped, one-eighth-inch wide holes in the bark of ash trees. The Westmoreland infestation was discovered by one of the 20 crews dispatched in Pennsylvania this summer to assess the beetles' spread.

People who suspect they have seen an emerald ash borer should call the Agriculture Department's pest hotline at 1-866-253-7189.