Ultrastructure and development of single-walled sensilla placodea and basiconica on the antennae of the Sphecoidea (Hymenoptera : aculeata)

While the pore plates of some species of the Sphecoidea (Hymenoptera) rise above the antennal surface, those of other species are flush with it. Not all species possess pore plates. On the antennae of those species, which lack pore plates, small sensilla basiconica are found. The pore plates of Psenulus concolor were studied in detail. The cuticular apparatus rises above the antennal surface. Cuticular features are the encircling ledge and delicate cuticular ledges reinforcing the perforated plate, as well as a joint-like membrane that anchors the plate into the antennal cuticle. Each pore plate is associated with 9–23 sense cells and 4 envelope cells, the second of which is doubled. In very early developmental stages, however, supernumerary envelope cells are observed; they degenerate before the cuticulin layer is secreted. Envelope cell 1 secretes a temporary dendrite sheath, while the envelope cells 2–4 are responsible for the secretion of the cuticular apparatus.The morphology and the development of the small sensilla basiconica are described in Trypoxylon attenuatum. The curved sensillum pointing to the tip of the antenna is anchored by a joint-like membrane. About 15 sense cells innervate the sensillum. The number and the arrangement of the envelope cells resemble that of the sensilla placodea. During very early developmental stages, supernumerary envelope cells are also observed. They degenerate before the cuticle of the cone is secreted by the surviving envelope cells 2–4.