An invasive insect is killing the red pines of Acadia National Park

Red pines make up only a small part of Acadia's forests, and most of them are now dead or dying. The cause is the red pine scale, an invasive insect that Acadia National Park staff found near Norumbega Mountain, in the town of Mount Desert, in September 2014. It was the first known occurrence in the State of Maine. Park staff and nearby residents had watched red pine decline in and around Acadia for more than a decade before anyone knew why.

Patches of red pine scale insect on a red pine branch. NPS photo.

The insect

The red pine scale (Matsucoccus matsumurae), also called the Japanese pine bast scale, is native to Japan and arrived in the United States in 1946. The insect is about the size of a pinhead and covers itself in a protective white, woolly substance that shows on branches. It is one of the most significant pests of native red pine, but it does not affect the other pine species native to Maine.

Red pine is found in patchy stands across the Mount Desert Island district of the park and on private land. Besides giving value to wildlife, it is planted widely in New England for landscaping and for forest products. A large die-off also has a cost: many dead trees become hazards that must be removed, which can raise the work and expense of protecting public safety and utilities.

A Maine Forest Service employee uses a pole pruner to take a branch sample from a red pine infested with the scale. NPS photo.

How far it spread

Resource managers inventoried red pine stands in 2015 and found the scale more widely distributed across the island than first thought: it had essentially spread all over Mount Desert Island. An infestation turns pine needles crimson and drops them within two to three years.

Red pine mortality along the North Ridge Trail of Champlain Mountain, 2019. NPS photo.

Norumbega Mountain seen from Somes Sound: red pines dying in 2014 (top) and dead from red pine scale in 2019 (bottom). NPS photos.

Telling a red pine

• A tall, straight trunk whose lower branches fall off with age (self-pruning)
• Reddish-brown, plated bark
• Needles 4 to 6 inches long, two to a cluster, that break cleanly when doubled
• Egg-shaped cones about 2 inches long, without prickles

What Acadia is doing, and what visitors can do

Park managers are removing dead pines that threaten roads, trails and parking lots. Ecologists recommend leaving standing dead pines that are not hazards, so they can break down naturally; they shelter wildlife and return nutrients to the soil. Long-term monitoring will track the scale's spread and the changes in forest makeup after so many red pines die.

The park asks the public to report unusual insects or plant die-offs to Acadia resource managers or Maine state entomologists, since most reports of new invasive species come from concerned citizens. It also asks people not to move landscaping materials or forest products, firewood included, over long distances.

Where this belongs

• Acadia National Park

Sources

• National Park Service, Acadia National Park, "Red Pine Scale kills red pine trees at Acadia" (https://www.nps.gov/articles/red-pine-scale-acadia.htm); rewritten in hubnx's own words.