Honeybee workers reared in standard-cell combs have larger hypopharyngeal glands

The functionally and morphologically variable hypopharyngeal glands (HGs) of honey bee Apis mellifera workers play critical roles in the individual bee physiology and honey bee colony biology. Previous studies have primarily focused on the age polyethism of honeybees involved in undertaking colony activities, including foraging or guarding, as life expectancy decreases. However, the development of the role of these glands in the life of a bee, and thus the division of labour in the colony, is also conditioned by environmental factors. The aim of the study was to investigate the impact of the comb cell size (small-cell or standard-cell comb) in which worker bees were reared on HG acini count and size (width, length and area) of worker bees on 1-, 7-, 14- and 21 days of their life. The acini of workers reared in small-cell combs (4.96-4.97 mm) (SM-bees) had significantly smaller width and length and, therefore, acini area, than workers reared in standard-cell combs (5.54-5.56 mm) (ST-bees). Bees reared in standard-cell combs had, on average, higher acini number in the HGs 500 µm collecting duct distance. The results presented in the current work thus suggest the occurrence of anatomical and morphological differences caused by the type of comb. The higher number of ST-bee acini and the higher width, length and area of HG acini found during workers' development compared to SM-bees suggests that workers reared in standard-cell combs are predisposed to perform various tasks in the nest, mainly as nurse bees or as nectar converters. In contrast, workers reared in small-cell combs seem better suited for working outside the nest, taking on the role of foragers. It seems that the presence of morphological polyethism induced by rearing conditions during larval and pupal development results in sub-cast specialisation and individual bee functionality. Verification of the above hypotheses may determine new research directions on explaining the mechanisms of functioning of the complex socio-physiological system created by the honeybee colony - the superorganism.