Variation in North American bumble bee nest success and colony sizes under captive rearing conditions

Of the 265 known bumble bee (Bombus) species, knowledge of colony lifecycle is derived from relatively few species. As interest in Bombus commercialization and conservation grows, it is becoming increasingly important to understand colony growth dynamics across a variety of species since variation exists in nest success, colony growth, and reproductive output. In this study, we documented successful nest initiation and establishment rates of colonies produced from wild-caught gynes, and created a timeline of colony development for fifteen western North American Bombus species captively reared from 2009 to 2019. Additionally, we assessed variation in colony size among five western North American Bombus species from 2015 to 2018. Nest initiation and establishment rates varied greatly among species, ranging from 5–76.1% and 0–71.8%, respectively. Bombus griseocollis had the highest rates of nest success across the eleven-year period, followed by B. occidentalis, B. vosnesenskii, and B. huntii. Further, we identified that colonies reared from two gynes had significantly higher nest initiation and establishment rates per nest box compared to those reared from a single gyne. Colony size also differed significantly among species with B. huntii and B. vosnesenskii producing more worker/drone cells than B. griseocollis, B. occidentalis, and B. vancouverensis. Additionally, gyne production differed significantly among species with B. huntii colonies producing more gynes than B. vosnesenskii. Results from this study increase knowledge of systematic nesting biology for numerous western North American Bombus species under captive rearing conditions, which can further improve rearing techniques available to conservationists and researchers.