Electron microscopic studies of antennal sensilla in the ambrosia beetle Trypodendron lineatum (Olivier) (Scolytidae)

Abstract

The antennae of the ambrosia beetle Trypodendron lineatum (Olivier) were examined with the light and electron microscopes to determine the types, distribution, and structure of sense organs found thereon. Six main types of sense organs are present, with an additional seventh cuticular structure, the hypodermal gland pore, which is thought to be non-sensory.Sensilla chaetica possess one bipolar neuron terminating in a scolopale at the base of the thick-walled articulated hair.Type I sensilla trichodea are short articulated hairs of unknown fine structure and innervation.Type II sensilla trichodea are sharp-pointed hairs of intermediate length, with thin, perforated hair walls, and two neurons with slightly branched dendrites in the hair lumen.Type III sensilla trichodea are blunt-tipped, reversely curved hairs possessing a double lumen and four to seven bipolar neurons, the unbranched dendrites of which extend to the hair tip.Sensilla basiconica are short thin-walled perforated hairs or pegs, possessing two neurons each, with many-branched dendrites. The relationship of dendrite branches to hair perforations is not clear.Sensilla campaniformia consist of a subsurface dome in the center of which lies the nerve ending of one neuron similar to that of the sensilla chaetica.Evidence is presented, indicating the probable absence of sensory axon fusion in the antennae.