Impact of Monofloral Pollen Diets on the Development of Hypopharyngeal Glands and Modulation of Enzymatic, Non-Enzymatic, and Ionic Biomarker Activities in Selected Fat Body Segments and Hemolymph of Apis mellifera Workers

The homogenization of landscapes and reduction in floral diversity have increasingly led to low diversity in pollen diets for honey bees. In this study, we examined the effects of monofloral pollen diets based on wind-pollinated (Corylus sp., Pinus sp.) and insect-pollinated plants (Brassica napus L., Phacelia sp., Solidago sp., Fagopyrum sp.) on the development of hypopharyngeal glands (HPGs), activities of enzymatic (AST, ALT, ALP, GGTP) and non-enzymatic (urea, uric acid) biomarkers, as well as magnesium, calcium, and phosphorus concentrations in the hemolymph and fat bodies from different locations (tergite 3, 5 and sternite) in worker bees. Even a small (10%) addition of pollen to sugar candy stimulated the development of acini compared to the control group, with phacelia, buckwheat, and goldenrod pollen having the strongest effects. The largest acini developed in the 14-day-old bees fed with Phacelia pollen, whereas the collecting duct diameters were significantly reduced in all the pollen-supplemented groups. Enzymatic biomarker activities were the highest in the hemolymph of newly emerged bees and increased with age across all the tissues, particularly in tergite 5, with the highest activities recorded in the bees fed with insect-pollinated plant pollen. Non-enzymatic parameters and ion concentrations also varied with tissue type and segmental location, generally increasing with age and reaching the highest values in tergite 5. Regardless of the tissue (the fat body vs. hemolymph), the bees fed a diet containing pollen from Brassica napus, Phacelia, Solidago, and Fagopyrum had higher concentrations of calcium, magnesium, and phosphorus, while the effects of hazel and pine pollen were less pronounced. These findings suggest that even limited pollen supplementation can positively shape the morphological and biochemical physiology of worker bees. Understanding these relationships is crucial for developing strategies to support bee health under increasing environmental pressures and changing floral availability.