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

Abstract

β-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 β-glucans administered orally for 96 h on Apis mellifera workers (newly emerged and nurse bees). β-glucans were included in honey and syrup. Survival rate and phenoloxidase activity were measured. In both newly emerged and nurse bees, β-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 β-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 β-glucans and the control group (p > 0.05). The absence of significant variation in survival suggests that the potential negative effect of β-glucans in healthy bees could be mitigated by their metabolism. Conversely, the inclusion of β-glucans in a honey-based diet determined an increase of phenoloxidase activity, suggesting that the effect of β-glucan inclusion in the diet of healthy bees on phenoloxidase activity could be linked to the type of base-diet. Further investigations on β-glucans metabolism in bees, on molecular mechanism of phenoloxidase activation by 1,3-1,6 β-glucans, and relative thresholds are desirable. Moreover, investigation on the combined action of honey and β-glucans on phenoloxidase activity are needed.

Effects of Two Commercial Protein Diets on the Health of Two Imago Ages of Apis mellifera L. Reared in Laboratory

“…In addition, the same diet group at the 20th day also showed the highest mortality rate, which suggests that bee mortality could be linked to a low basal activity of phenoloxidase. This result is in accordance with the hypothesis that bee survival is positively linked to a high basal activity of phenoloxidase [20,38,45]. Therefore, the intake of an excess of proteins could affect any point in the enzyme cascade or even its regulation; therefore, further investigations to clarify the mechanism linking the protein diet concentration to the decrease of phenoloxidase are needed.…”

Queen Caging and Oxalic Acid Treatment: Combined Effect on Vitellogenin Content and Enzyme Activities in the First Post-Treatment Workers and Drones, Apis mellifera L.

“…In both workers and drones, phenoloxidase activity was not significantly affected by the experimental treatment. As phenoloxidase belongs to the individual innate immune system of honey bees, it is not surprising that individuals from healthy colonies did not show altered patterns in the activity of this enzyme [ 19 , 29 , 36 ].…”