Comparative survival and fitness of bumble bee colonies in natural, suburban, and agricultural landscapes

Abstract

Pollinators such as bumble bees are in decline as a result of many factors, including loss of habitat. Initiatives to improve and restore pollinator habitat are increasingly popular. However, to most effectively conserve pollinators, we need a better understanding of which habitats limit their survival and fitness at the landscape scale. Our study examined performance and fitness of the common eastern bumble bee, Bombus impatiens (Cresson), in four common landscapes for bees (natural, suburban, conventional agriculture, and organic agriculture). In the summers of 2016 and 2017, 64 bumble bee colonies per year were deployed across 16 sites (4 sites in each landscape type in each year) and their growth (weight and bee abundance), fitness (caste production), and survival were monitored weekly. Colonies in suburban sites in 2016, but not 2017, were lighter, produced fewer worker and drone cells, and experienced queen death more quickly than colonies in natural and agricultural landscapes. The performance and fitness of colonies in natural, organic agricultural, and conventional agricultural landscapes in both years were similar. Additionally, across all landscape types, the proportion of developed land and impervious surface were significantly negatively associated with colony performance in 2016. Thus, our results suggested that suburban landscapes are suboptimal for B. impatiens compared to natural and agricultural landscapes, and that this effect differs across years, potentially due to climactic differences. Future research is needed to identify the mechanisms responsible for reduced performance of bumble bee colonies in suburban landscapes, especially regarding floral resources and pesticide and pathogen stress. Such information could direct specific actions to improve suburban habitat for pollinators.