Ultrastructure of the lateral and medial galeal sensilla of the larva of the red turnip beetle, Entomoscelis americana brown (Coleoptera : Chrysomelidae)

Abstract

The structures of 2 sensilla on the larval galea are described. Both sensilla have multiple innervation and one of them, the lateral sensillum, is known to be a contact chemosensillum. The function of the second, medial sensillum, is unknown. This study was undertaken to provide information needed for interpretation of electrophysiological data on the lateral sensillum and to shed some light on the function of the medial sensillum. The lateral sensillum is uniporous and is innervated by 5 cells, one of which has a well-developed tubular body and ends near the sensillum socket, while the remaining cells communicate with a pore in the sensillum tip. The medial sensillum is innervated by 2 cells, neither of which has an apparent tubular body. Both of these cells have dendrites that run to the sensillum tip. No pore has been demonstrated in the tip of the medial sensillum by scanning and transmission electron microscopy and electrophysiological techniques. This sensillum is also unusual in that it has no apparent distal dendritic sheath. Its structure is compared with that of similar sensilla in other insects and some of its possible functions are considered.