The conservation status of Bombus moderatus and B. occidentalis (Hymenoptera: Apidae) in Alaska, U.S.A

In both Canada and the contiguous U.S.A., species of the subgenus Bombus sensu stricto are experiencing dramatic declines in abundance and range. However, virtually nothing is known on the status of the two species of Bombus s. str. that co-occur in the Alaskan Interior: B. moderatus and B. occidentalis. This study presents a status snapshot of both species by investigating their relative abundance, Nosema bombi pathogen loads and distribution in the Alaskan Interior. Bombus occidentalis and B. moderatus account for 36% and 11% of the bumble bee fauna surveyed, respectively. While B. occidentalis was the most abundant species in our survey, it also had the highest proportion of N. bombi infections (44% infected), whereas the proportion of infected B. moderatus did not differ significantly from co-occurring bumble bees. Despite N. bombi infections, our investigation suggests that both species are detectable in the Alaska Interior, particularly B. occidentalis, with our survey method. Finally, we present their potential distributions in Alaska utilizing species distribution modeling techniques, as well as identify Alaskan ecoregions where the probability of occurrence is the highest.