The Maine Forest Service expanded its emerald ash quarantine zones to include all towns on Mount Desert Island.

The quarantine follows the discovery of a “well-established” population of emerald ash borers, an extremely invasive wood-boring beetle that kills nearly all species of ash trees in Maine, the Maine Forest Service said Tuesday. Ash trees make up about 4% of Maine’s hardwood and about 2% of its overall forest, according to the Department of Agriculture, Conservation and Forestry.

State Forester Patty Cormier said the species’ discovery was “unfortunate but not entirely unexpected.”

While under quarantine, all ash tree material should remain on the island, not including wood chips, which are not regulated, the service said. Infested trees are likely to become structurally unstable, and owners should consider treating or removing them, the service said.

Emerald ash borer was first spotted in Maine in 2018.

“Emerald ash borer is one of the most damaging forest pests we face,” Cormier said. “By working together — with awareness, early detection, and coordinated response — we can slow its spread and protect Maine’s forest resources.”