Fine structure of surface and sunken grooved pegs on the antenna of female Anopheles stephensi (Diptera: Culicidae)

Abstract

The antenna of female Anopheles stephensi Liston bears three types of sensilla with grooved pegs: those sunken in pits and subtypes A and B of those located on the flagellar surface. The sunken peg sensilla are innervated by four or five neurons with branching dendrites. The dendrites are exposed to the exterior by means of longitudinal clefts at the bases of the grooves in the peg wall. Surrounding the dendrites and extending into the clefts is an extracellular material of medium electron density. Three sheath cells are associated with each sunken peg sensillum.Subtype-A surface peg sensilla are generally similar to the sunken peg sensilla, except that they are located on the antenna) surface and are innervated by two neurons with unbranched dendrites. Subtype-B surface peg sensilla have three or four neurons, the dendrites of which do not branch and are exposed less to the exterior than those in the other peg sensilla because the clefts in the peg wall are smaller and less frequent. Only trace amounts of electron-dense material occur in the clefts of the subtype-B surface peg sensilla.The sunken peg and both subtypes of the surface peg sensilla are probably olfactory receptors.