AGE-RELATED ULTRASTRUCTURAL CHANGES OF THE THORACIC LABIAL GLAND OF APIS MELLIFERA CARNICA WORKERS (HYMENOPTERA: APIDAE)

Abstract

In the eusocial insects, the exocrine system controls the tasks during their lifespan. This appears as structural and functional changes of the glands with age. The thoracic labial (salivary) gland of Apis mellifera carnica worker synthesizes and secretes saliva containing digestive enzymes. The changes of the gland ultrastructure were studied with respect to age. The gland is tubular and the secretory tubes consist of parietal and secretory cells arranged around a central canal and subcuticular space with a canalicular system. The cells contain electron-dense and clear secretory vesicles, plenty of mitochondria and apical microvilli. In nurses, the secretory tube diameter increases and the subcuticular space widens with age due to the filling with secretion, and reachs the maximum values at an age of 15-days and decreases in foragers, while the epithelium thickness decreases alongside with their increases and vice versa, probably due to the discharge of secretion. The largest diameter and the highest number of secretory vesicles were recorded in 15-day old workers. This coincides with converting nectar to honey, wax softening, queen cleaning and nursing tasks of the worker. The thoracic labial gland exhibits an age-dependent secretory cycle. Although the secretory vesicles decrease in diameter in 27-days old workers, there is an increase in number. Therefore, the aged foragers try to increase the secretory activity of their glands to cope with the colony needs, which indicates the gland flexibility. Further investigations are needed to explicit all putative functions of the gland.