Age-dependent morphology and ultrastructure of the thoracic labial gland of Apis mellifera carnica Pollm. workers (Hymenoptera, Apidae)

Exocrine glands are well developed in social Hymenoptera and play an important role in the social life of these insects. We studied the thoracic labial gland of Apis mellifera carnica Pollm. in relation to age. We observed two cell types in the secretory tubes of the thoracic salivary gland : parietal and secretory cells. In the secretory cells, two types of secretory vesicles occur. Abundant mitochondria, vesicles and apical microvilli indicate that parietal cells also have a secretory function. The size of the subcuticular space increases with age, probably by filling with secretion. We found differences in the numbers of secretory vesicles between summer and winter bees. Probably, these vesicles accumulate in winter bees, and glands do not discharge their secretion until spring.