Sensory Receptors on the Forceps of the Male imago and subimago of Ecdyonurus venosus (Ephemeroptera: Heptageniidae)

The ultrastructure of the globular papillae located along the inner side of the forceps of the two flying stages, imago and subimago, of male mayflies belonging to Ecdyonurus venosus (F.) is described. The external shape of the globular papillae varies with their position on the forceps’ segments and the stage. In longitudinal section, the globular papillae of the imago and subimago have a single dendrite ending in a tubular body, a feature consistent with their function as mechanosensory sensilla. During mating, the mechanical pressure on the forceps may be sensed by the cuticular surface of the papillae and transmitted to the tubular body. In the subimago, the globular papillae have a pointed apex and are less numerous. Another kind of sensillum, hairs having the typical organization of mechanoreceptive bristles, are scattered on the forceps of both imago and subimago.