The histological architecture of the auditory organs in the parasitoid fly Ormia ochracea

Gravid females of the parasitoid fly species Ormia ochracea (Diptera: Tachinidae) rely on their sense of hearing to detect and localize their hosts, field crickets of the genus Gryllus. As in any hearing insect species, the fly's auditory system consists of a rather complex cascade of mechanical and physiological mechanisms, starting with the conversion of the acoustic energy in the sound field into mechanical vibrations that, in turn, are sensed in the auditory sensory organs by multicellular mechanoreceptive units - the scolopidia. This article reports on the histological architecture of the sensory organs using conventional histological serial sections and their three-dimensional reconstructions, and confocal laser microscopy. The scolopidia's spatial distribution and the three-dimensional organization of the actin-containing attachment cells are described. Morphometric measurements show that individual scolopales vary in their size and shape. Pronounced intersexual differences have been previously shown to exist in auditory function, in particular with respect to frequency sensitivity, peripheral auditory anatomy, and notably behavior. The present results show that intersexual differences in the histoarchitecture of the sensory organs are small. Results are compared with some other insect auditory systems and are also discussed in terms of their significance for frequency sensitivity.