The effects of heavy metals on the common eastern bumblebee, Bombus impatiens

Heavy metal contamination is a byproduct of many industrial and urbanization processes and has been found to have negative and prolonged impacts on biota. Cities are oftentimes contaminated with heavy metals, however, also support a diversity of bee species. Currently, little is known about the impacts of heavy metal contamination on bee fitness. Bumblebees are prolific pollinators that are common in cities and whose foraging behavior potentially exposes them to a plethora of contaminants such as heavy metals (HM). We examined how exposure to environmentally-relevant concentrations of the HMs arsenic and lead within nectar sources influence bumblebee brood survivorship. Using HM concentrations from bumblebee-collected honey in hives located in Cleveland, OH we developed a replicated foraging experiment to measure the fitness effects of these contaminants. We conducted 15 d and 30 d foraging experiments within twelve 13.5 m3 tents with three nectar treatments: arsenic (0.84 mg/L, n=4), lead (0.265 m/L, n=4), and an uncontaminated control (n=4). Treatments were arranged in a randomized design. Each tent contained a nectar feeder with respective HM concentrations, a pollen feeder, and one colony with approximately 70 workers, allowed to forage ad libitum. After the exposure periods, all colonies were weighed, dissected, and brood and adults counted. We found similar brood abundance across treatments, but a significantly higher proportion of dead brood in HM exposed hives. These data illustrate that even environmentally relevant concentrations of HMs found within cities can negatively influence bee fitness and threaten the value of bee-focused urban conservation efforts.