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

• Main Authors: Simona Sagona, Baldassare Fronte, Francesca Coppola, Elena Tafi, Matteo Giusti, Lionella Palego, Laura Betti, Gino Giannaccini, Lorenzo Guglielminetti, Antonio Felicioli
• Format: Article
• Language: English
• Published: MDPI AG 2021-07-01
• Series: Veterinary Sciences
• Subjects: <i>Apis mellifera</i>; β-glucans; innate immune system; nutrition; survival; phenoloxidase activity
• Online Access: https://www.mdpi.com/2306-7381/8/7/130

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 <i>Apis mellifera</i> 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 (<i>p</i> > 0.05). Conversely, phenoloxidase activity was higher in both newly emerged bees (<i>p</i> = 0.048) and nurse bees (<i>p</i> = 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 (<i>p</i> > 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.