Effect of Honey and Syrup Diets Enriched with 1,3-1,6 ß-Glucans on Honeybee Survival Rate and Phenoloxidase Activity (Apis mellifera L. 1758).

ABSTRACT

ß-glucans can activate the animal innate immune system by acting as immune-modulators and inducing various stimulatory effects. The aim of this study was to investigate the effect of 1,3-1,6 ß-glucans administered orally for 96 h on Apis mellifera workers (newly emerged and nurse bees). ß-glucans were included in honey and syrup. Survival rate and phenoloxidase activity were measured. In both newly emerged and nurse bees, ß-glucans supplementation did not affect survival rate (p > 0.05). Conversely, phenoloxidase activity was higher in both newly emerged bees (p = 0.048) and nurse bees (p = 0.014) fed with a honey diet enriched with ß-glucans compared to those fed with only honey. In both the newly emerged and nurse bees, no statistical differences in phenoloxidase activity were recorded between the group fed with a syrup-based diet enriched with ß-glucans and the control group (p > 0.05). The absence of significant variation in survival suggests that the potential negative effect of ß-glucans in healthy bees could be mitigated by their metabolism. Conversely, the inclusion of ß-glucans in a honey-based diet determined an increase of phenoloxidase activity, suggesting that the effect of ß-glucan inclusion in the diet of healthy bees on phenoloxidase activity could be linked to the type of base-diet. Further investigations on ß-glucans metabolism in bees, on molecular mechanism of phenoloxidase activation by 1,3-1,6 ß-glucans, and relative thresholds are desirable. Moreover, investigation on the combined action of honey and ß-glucans on phenoloxidase activity are needed.