Bumble bees (Bombus spp., Hymenoptera: Apidae) of Rhode Island: species richness, relative abundance, and floral visitation.

Abstract

Historical records (1900 to 1999) indicate that 12 bumble bee species occurred in Rhode Island, however, baseline data of current bee fauna are limited. To assess the status of bumble bee species in Rhode Island, a statewide survey was conducted by visual observations of bees visiting flowers and using vane traps. Floral observations in 2020 and 2021 were conducted to document flowering plant visitations and bumble bee species richness and abundance. Bees were collected using vane traps at farms, golf courses, and residential areas throughout the state from 2019 to 2021. Non-Bombus bees collected in vane traps were also identified. Pollen from historical and modern bumble bee specimens were analyzed to establish a floral association species record. Among 12 historical Bombus species documented from Rhode Island, B. affinis Cresson, B. citrinus Smith, B. pensylvanicus DeGeer, B. ternarius Say, or B. terricola Kirby were not found, suggesting rarity or current absence. Bombus impatiens Cresson was the most abundant survey species, while B. auricomus Robertson, a new state record, was least abundant. Bombus species richness was highest on Monarda fistulosa L., Trifolium pratense L., and Lavandula angustifolia Mill, and M. fistulosa had the highest bee visitations. Blue vane traps purchased in different years from the same company differed significantly in bee captures (both Bombus and non-Bombus), indicating that caution is needed when assessing bee populations with seemingly standardized trapping methods. This study provides baseline data regarding the current status of Rhode Island bumble bees that will be critical to implementing conservation practices for declining species.