Supplemental carbohydrates influence abiotic stress resistance in honey bees

Authors: MOGREN, CHRISTINA - LSU Agcenter; MARGOTTA, JOSEPH - LSU Agcenter; Danka, Robert; OTTEA, JAMES - LSU Agcenter; HEALY, KRISTEN - LSU Agcenter

Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: Beekeepers often feed sucrose syrup (SS) or high-fructose corn syrup (HFCS) to honey bee colonies as emergency rations or to stimulate population growth. However, these carbohydrates lack some nutrients present in nectar and honey and thus may stress colonies nutritionally. We investigated how honey bees respond to the common environmental stressors of heat (45°C), cold (4°C), and exposure to the insecticide imidacloprid after young bees had been fed either honey, SS, HFCS, or HFCS plus natural pollen for five days; some bees were left unstressed. In laboratory trials, the longevity of bees exposed to heat or cold was not affected by the carbohydrate diet given in early adulthood. However, in bees fed SS, unstressed bees had greater longevity than bees stressed by imidicloprid. Concentrations of three stress proteins were measured to determine sublethal effects on bees. The concentrations of the stress proteins were affected both by the type of diet and by the type of stress, but these responses were inconsistent among the three proteins measured. In a field trial, bees fed SS had reduced longevity compared to bees that were fed other carbohydrate sources. In both lab and field trials, bees consumed more honey and HFCS plus pollen than SS or HFCS alone. Together, these results suggest that diets with honey and HFCS plus pollen are preferable to supplemental carbohydrates alone. Where possible, beekeepers should locate apiaries near sufficient wild forage, or provide protein supplements to mitigate the effects of other environmental stressors.

Technical Abstract: During periods of pollen and nectar dearth, beekeepers may provide supplemental food in the form of sucrose (SS) or high-fructose corn syrup (HFCS), and artificial pollen. However, these carbohydrates 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 these supplemental sources 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 longevity 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 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 semi-field 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.