Ultrastructure of the larval antenna of Tenebrio molitor L. (Coleoptera: Tenebrionidae): structure of the blunt-tipped peg and papillate sensilla

Abstract

Each antenna of a final instar Tenebrio molitor larva has two blunt-tipped pegs and two papillate sensilla. The former are short pegs with fluted cuticle and a terminal moulting pore and are set in deep sockets. Two large microtubule-filled dendrites fill a dense dendritic sheath within the peg; below the base of the peg they are joined by a lamellate dendrite and a dendrite resembling a scolopidial cilium. There are four accessory cells, the innermost resembling a scolopale cell. This sensillum may be thermo- and hygro-receptive.Superficially the papillate sensillum is radially symmetrical with a central zone of small cuticular papillae surrounded by one or two rings of smooth cuticle. Three or four dendrites (of five) end under a turret of longer papillae at the center of the papillate cuticle. Fine pores from the dendritic canal extend to the surface between the papillae. One or two dendrites, one of which may be lamellate, end well below the end organ. There are five accessory cells. The sensillar and ciliary sinuses are large and the bounding membranes of the sheath cells highly elaborated. The function of this sensillum is uncertain.