NASHVILLE (AP) — The invasive emerald ash borer has been found in two more Tennessee counties.

The discoveries in Scott and Jackson counties bring to 21 the number of counties where infestations have been found in the state. Hamilton County was added to a quarantine list earlier this summer when the pest was found near a railroad hub.

The destructive insect was first found in Tennessee in 2010, when it was discovered near a Knox County truck stop.

The quarantine prohibits the movement of firewood, ash nursery stock, ash timber and other material that can spread the borer. State residents who find damage to ash trees should report it to the Tennessee Department of Agriculture.

The destructive insect has killed millions of ash trees across several states after first appearing 20 years ago.