Ultrastructural aspects of two sting glands in social Hymenoptera

Exocrine glands associated with the sting apparatus are widespread in social Hymenoptera. Well-known are the venom gland and the Dufour gland. However, some other glands have been reported in literature. One example is the `sting gland' in the region of the triangular plate part of the sting apparatus. This gland belongs to the secretory unit type 3. The duct cells open through an intersegmental membrane near the base of the triangular plate. In the present study, this site of duct openings is discussed in the perspective of its association with the oviduct and not with the sting sensu stricto. The postulated involvement of the gland in reproduction gains in importance, because obvious differences concerning glandular size were found between queens and workers. This tendency is observed for some ants, for bumblebees and for social wasps. In general, this triangular plate gland seems to metabolize lipids. The fact that some queens possess extremely developed glands most probably has little to do with lubricant production needed for facilitating the act of stinging, as is sometimes suggested in literature, since usually workers are more likely to sting throughout their lives, and queens will especially sting at the more critical stage of colony foundation. A second gland, the quadrate plate gland was found near the quadrate plate of the sting in bumblebees. Ultrastructural characteristics of both glands are described.