Recent declines of some bumble bee (Bombus) species has raised concerns about these important pollinators, igniting efforts to improve habitat. While the foraging patterns of bumble bees are well documented, less is known about the early colony life stages of bumble bee species. Nest establishment is a critical, but vulnerable stage because each queen works alone to establish a nest in spring. We tested the hypothesis that species differed in their nesting habitat and microhabitat preferences. We also hypothesized that species differed in their success at establishing nests as reflected by change in relative abundances of summer workers compared to spring queens. We conducted spring queen surveys of 108 sites across Ohio, USA, documenting habitat types and microhabitat features associated with nest searching behavior, and re-surveyed 53 of these sites for worker caste bees in summer. We compared the number of queens found per time unit among habitat types and the percent of nest searching queens associated with each microhabitat. To evaluate success of establishment among species, we compared the relative species abundances of queens to those of workers at a subset of sites surveyed in spring and summer.
Results/Conclusions
Bumble bee queen surveys conducted from May 1 to June 8, 2018 yielded 1089 bumble bee queens of nine different species; 451 of these were exhibiting nest searching behavior. Significantly more nest seeking queens per minute were found along field-forest edges and in maintained areas than in strictly wooded, field, or wetland habitats, a pattern driven by the dominant species, B. impatiens. Across species, individual nest seeking queens most often searched crevices in leaf litter (70.8 %), and less often near woody debris or tree bases (46.7 %), near flowers (35.6 %). in herbaceous plant debris (31.9 %), and in grass clumps (7.9 %). We did not detect differences among microhabitat preferences of the most abundant species of nest seeking queens (B. impatiens, B. griseocollis, and B. bimaculatus; the other six species were not abundant enough to analyze). At sites sampled twice, Bombus impatiens dominated both spring queen (60%) and summer worker (31%) surveys, and the most abundant three species (B. impatiens, B. griseocollis and B. impatiens) accounted for 92% of spring queens and 76% of summer workers. Lower dominance of B. impatiens in summer than in spring suggests that it is less successful in establishing nests than other species.