Morphology and ultrastructure of the Dufour gland in workers of social wasps (Hymenoptera, Vespidae).

The Dufour gland in workers of vespine wasps appears as an unpaired tubiform gland that opens in close proximity to the sting base. The epithelial cells that line the central reservoir are characterized by apical microvillus-like projections and deep basal invaginations. Their cytoplasm contains a well-developed Golgi apparatus, numerous mitochondria, as well as strands of smooth endoplasmic reticulum. The Dufour gland duct occurs ventrally to the venom gland duct, and bends downward near the sting base to open in the dorsal vaginal wall. In this region, the duct is dorsoventrally flattened, and shows conspicuous bundles of parallel microtubules in the epithelial cells, that transmit the pulling forces of the myofilaments of the underlying muscular supply to the cuticle. This results in an active opening mechanism regulated by muscular contraction, while passive closure probably results from the return of the cuticular intima to a rest position.