The venom apparatus in stenogastrine wasps: Subcellular features of the convoluted gland

In the wasp venom apparatus, the convoluted gland is the tract of the thin secretory unit, i.e. filament, contained in the muscular reservoir. Previous transmission electron microscope investigation on Stenogastrinae disclosed that the free filaments consist of distal and proximal tracts, from/to the venom reservoir, characterized by class 3 and 2 gland patterns, respectively. This study aims to extend the ultrastructural analysis to the convoluted tract, in order to provide a thorough, subcellular representation of the venom gland in these Asian wasps. Our findings showed that the convoluted gland is a continuation of the proximal tract, with secretory cells provided with a peculiar apical invagination, the extracellular cavity, collecting their products. This compartment holds a simple end-apparatus lined by large and ramified microvilli that contribute to the processing of the secretory product. A comparison between previous and present findings reveals a noticeable regionalization of the stenogastrine venom filaments and suggests that the secretory product acquires its ultimate composition in the convoluted tract. •We investigate external and ultrastructural morphology of the convoluted gland for the first time in two Stenogastrinae wasps.•Convoluted gland is a continuation of the venom gland, it is provided with Class 2 secretory cells showing peculiar features.•Convoluted gland produces late hydrophobic components of the poison.•Ultrastructural features of convoluted gland are shared by different Vespidae eusocial subfamilies.