Seasonal variation of flavonoid content in bee bread: Potential impact on hypopharyngeal gland development in Apis mellifera honey bees

Bee bread is the main source of proteins necessary for the development of hypopharyngeal glands in nurse bees. However, the seasonal chemical composition and its effects on honey bee physiology are poorly understood. Thus, this study evaluated how the season and botanical origin of pollen influence the content of crude protein, ash, and total flavonoids, as well as the profile of flavonoids, in Africanized Apis mellifera bee bread. The influence of these factors on the number and area of hypopharyngeal gland acini of nurse bees raised with similar numbers of brood frames over the four seasons of the year were also evaluated. The botanical families found in bee bread and the total flavonoid content and their chemical profile varied markedly with the seasons of the year, with the highest total flavonoid content found in the summer. The percentage of crude protein and ash in bee bread, however, did not change with the seasons. The number and area of acini in the hypopharyngeal gland significantly decreased during autumn and winter. Based on our results, flavonoids rather than crude protein may play a role in hypopharyngeal gland development in honey bees. Further studies to test artificial diets supplemented with flavonoids can improve beekeeping strategies and contribute to colony maintenance in periods of food shortage.