The contribution of human foods to honey bee diets in a mid-sized metropolis

Concern for honey bee health has implicated both urbanization and nutritional stress as factors contributing to honey bee declines. The expansion of urban areas has resulted in reduced foraging habitat for bees, while at the same time introducing new food sources, such as foods unintentionally provided by humans as litter or in waste containers. While human foods play an important role in the diets of other urban animals, the extent to which honey bees feed on these resources has not been well characterized. Here, we compared the amount of human foods in honey bee diets across a rural-urban gradient in North Carolina, USA, using stable isotopes of carbon (d13C). Human-produced sugars—primarily sugarcane and corn syrup—have a characteristic isotope signature that can be used to quantify the relative amount of human foods in animal diets. We predicted that urban bees would have an increase in d13C if they were feeding on human-produced sugars, but we found no change in d13C between urban and rural colonies. Instead, we found an increase in d13C in managed bees in both habitats, which is indicative of supplemental sugar feeding by beekeepers. Rather than switching to human food sources, urban bees seem to be feeding on urban ?owers or insect-produced honeydew. This suggests an important role for urban ?owers and green spaces in maintaining healthy pollinator populations in cities.