The effect of proximity to a honeybee apiary on bumblebee colony fitness, development, and performance

Competition between managed honeybees and wild pollinators is thought to be a key factor in structuring foraging communities on flowers. The majority of studies have focused on impacts such as floral visitation rates and resource overlap. However, direct measurement of fitness is required to fully assess the impacts of competition. We compared in 2 years the weight and reproductive success of bumblebee colonies located at two sites that were either close to or far from a large honeybee apiary, and which were located in the same landscape and with access to similar floral resources. We found that bumblebee colonies located at the site near the honeybee apiary gained less weight, and produced fewer and smaller queens, in both years than colonies at the site far from the apiary. The ratio of queen weight/size was lower in the colonies near honeybees in 1 year, while males were smaller and offspring sex ratio more male biased in colonies close to honeybees than in those far from honeybees. Proximity to managed honeybee hives was therefore associated with significantly reduced fitness of bumblebee colonies, but studies from many more sites are needed to confirm the effect.