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Plant-Insect Ecosystems

Poster: P-IE, Ecology

D3437: Expansion of the eastern bumble bee Bombus impatiens (Cresson) in British Columbia and Washington State

Tuesday, November 12, 2024
9:00 AM – 5:00 PM MST
Location: Phoenix Convention Center, Exhibit Hall 6, PCC
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The common eastern bumble bee Bombus impatiens (Cresson) is among the most frequent bumble bee species cultivated for greenhouse and field deployment. The species was detected in the wild in British Columbia in 2006, presumably after escaping from greenhouse use. It has since spread throughout the area, reaching Washington State by 2013 and apparently established as far south as Skagit County. The species now accounts for between 20% and 30% of all community naturalist observations in the Fraser lowlands, but a much smaller fraction in adjacent Whatcom County. We used bycatch from giant hornet surveys, community naturalist observations, and net survey data from 2022-2024 to estimate rates of spread and search for landscape characteristics that may influence that spread. Initial analysis suggests that the bee has expanded its PNW range at a rate between 4 and 7 km per year, depending on direction and detection probability. This estimate does not account for possible re-introduction via commercial greenhouses. Molecular data indicate that the species is breeding naturally and does not appear to be impacted by Allee effects. There is some evidence that landscape features may have influenced expansion rates, with developed cover types associated with faster spread. Forested areas and/or higher elevation landforms may have slowed its southward spread, but recent detections indicate that B. impatiens has expanded beyond these putative barriers and is poised to rapidly expand throughout the Puget Sound.