ALASKA—Alaska Region entomologist Elizabeth Graham is keeping a close eye on an ongoing insect outbreak on the Tongass National Forest. 

After a 30-year break, the western black-headed budworm is back to creating damage in Southeast Alaska, causing the hemlock to turn reddish-brown.

The Forest Health Protection team heard about the insect’s activities prior to conducting its annual aerial surveys to detect changes in the forest.  
Thanks to reports from the public and district staff, the team had a good idea of where to fly and conduct their surveys this time around.  

The survey data is still being processed, but the hardest hit areas include Admiralty, Baranof, Kuiu, Kupreanof, Mitkof, Prince of Wales, Wrangell and Zarembo islands, as well as several drainages on the mainland as far north as Juneau.

Western black-headed budworms are one of the major disturbance agents on the Tongass National Forest. Caterpillars feed on the buds and new growth of hemlock, and then tie needles together to create the red appearance.

Some trees may not survive the damage caused by outbreaks. Those that do may benefit in the long-term with increased light and a nutrient boost to the forest floor. Topkill commonly occurs in heavily impacted areas and in extreme cases mortality can occur.

Western black-headed budworm outbreaks recur periodically in Southeast Alaska. The most recent took place in the mid-1990s, impacting the forested area between Frederick Sound and Juneau. Prior to that, an outbreak in the 1950s was said to have affected nearly every forested acre of the Tongass. The results of these outbreaks were topkill and scattered areas of mortality.

As the budworms turn into moths in the coming weeks, Alaska Region entomologists are looking for help tracking the insects to learn more about what next year’s budworm population may look like.

Several methods are used to track insect activity, including a platform familiar to the public, iNaturalist, which is a social media platform that allows users to upload observations. Data related to sightings of the insect and tree damage are automatically uploaded into the Alaska Forest Health Observations Project.

“We are hoping to improve our monitoring with the public being our eyes on the ground,” said Graham. “We plan to use those observations in our national reports on forest health.”