Supplemental carbohydrates influence abiotic stress resistance in honey bees

Abstract

During periods of pollen and nectar dearth, beekeepers may provide supplemental foods in the form of sucrose (SS), high-fructose corn syrup (HFCS), or artificial pollen. However, these lack micronutrients present in nectar and honey, and thus may nutritionally stress colonies. Given the many stressors faced by honey bees in the environment, we evaluated how honey bees fed supplemental carbohydrates responded in combination with heat (45 °C), cold (4 °C), or imidacloprid (0.48 ng/ml) exposure. Bees were fed either honey, SS, HFCS, or HFCS + pollen and then exposed to abiotic stress treatments in the lab. Hive bee mortality was not affected by heat or cold stress, but mortality was greater for bees fed SS in imidacloprid treatments. Levels of stress proteins (superoxide dismutase (SOD), heat shock protein (HSP70), and potentially esterase) were quantified to determine sublethal stress. SOD levels were reduced in SS and HFCS treatments, indicating these diets impaired a response to oxidative stress, particularly at 45 °C. HSP70 levels were higher in the imidacloprid treatment, with no differences between control and temperature treatments. Diet interacted significantly with stress treatment with generally negative responses to HFCS. There was no effect of diet on esterase levels, though activity was much lower at 4 °C. In semifield trials, colonies with newly emerged bees fed SS experienced higher rates of worker mortality. In cage and field trials, bees consumed significantly more honey and HFCS + P than SS and HFCS. Together, these results suggest that supplemental carbohydrates contribute to sublethal stress, and natural food sources are preferred.