Vitamin-protein supplementation influences hypopharyngeal gland hypertrophy in caged worker honeybees (Apis mellifera mellifera)

Honeybee colonies in Mongolia experience harsh environmental conditions and limited pollen availability, which can negatively affect worker physiology and colony productivity. This study evaluated the effects of vitamin-enriched protein supplementation on the hypertrophy of hypopharyngeal glands (HPGs) in worker honeybees (Apis mellifera mellifera) under controlled laboratory conditions. Newly emerged workers were randomly assigned to two control groups and three experimental groups receiving protein diets supplemented with vitamins at 1%, 2%, and 3%. The vitamin-protein supplement contained 21.0% protein, 7.1% fat, 2.6% ash, and a balanced amino acid profile enriched in phenylalanine, lysine, arginine, hydroxyproline, sarcosine, and proline. Average feed intake did not differ significantly among groups, indicating that diet quality, rather than quantity, influenced outcomes. HPG hypertrophy followed a typical ontogenetic pattern, peaking between days 6-12. Supplementation at 1-2% significantly increased acini diameter and surface area compared with controls, whereas 3% supplementation showed less consistent benefits, suggesting an optimal supplementation threshold. Protein nutrition alone improved gland hypertrophy, but vitamin enrichment further enhanced these effects. These results indicate that vitamin-protein supplementation may enhance hypopharyngeal gland hypertrophy under laboratory cage conditions.