Forest Services

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As growing spruce budworm populations continue to fluctuate in Maine, the Maine Forest Service, University of Maine Cooperative Forestry Research Unit (CFRU), and our cooperator network are tracking populations carefully in anticipation of an approaching outbreak.

A comprehensive spruce budworm (SBW) monitoring program requires a multi-pronged approach. It relies on using methods such as pheromone trapping, light trapping, overwintering L2 larval sampling, and both ground and aerial survey. At the core of the Maine Forest Service (MFS) monitoring program lies the extensive pheromone trap network throughout western and northern Maine's spruce-fir forests. A permanent pheromone trap network was first established in 1992. It was made up of 80 sites operated by MFS, J.D. Irving Ltd, Penobscot Nation Department of Natural Resources, and the USDA Forest Service. The program grew substantially in 2014, and since then, with the support of a large team of stakeholders, the pheromone trap network now consists of hundreds of sites.

SBW is a native insect whose outbreaks cover vast regions and spread through massive dispersal events as moths undergo atmospheric transport from impacted areas to new ones. In northeastern North America, SBW outbreaks tend to return on a 30-60 year interval, and the last major SBW outbreak to directly affect Maine occurred during the 1970s-80s. Historical data tells us that Maine is due for another SBW outbreak and monitoring efforts illustrate that over the last several years, SBW populations appear to have risen above endemic levels experienced between outbreak events. For several years now in Maine, both pheromone trap and light trap catches have been above numbers expected during the endemic period. Millions of acres of defoliation in neighboring Canadian provinces continue to encroach on the Maine border. From this outbreak area to the north, large in-flights of moths into northern Maine were well-documented in 2019. Atmospheric transport events of any appreciable scale largely lacked in 2020, however, meaning the majority of those moths recovered in 2020 have completed their life cycle here in Maine’s forests. Now that all major portions of the 2020 SBW monitoring season are complete, the first glimpses of how these 2019 mass migration events might impact Maine’s forests are being seen.



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