A novel hearing organ in an acoustic parasitoid fly

Female parasitoid flies (Ormiaochracea: Tachinidae) are attracted to singing male crickets [W. Cade, Science 190, 1312 (1975)]. Gravid female flies orient to calling crickets to deposit larvae, which burrow into the cricket in order to feed and grow to adulthood. To detect and locate cricket songs over long distances, these flies evolved a tympanal hearing organ previously unkown in flies. Electrophysiological recordings reveal low auditory thresholds (20 dB SPL between 4–6 kHz) matching the peak of the power spectrum of the host’s song (Gryllusrubens, 4.5–5 kHz). Such sensitivity is consistent with long distance hearing. The ear, composed of two adjacent thin tympanal membranes, contains two mechanoreceptive sensory organs that are both located in a single air-filled chamber. Laser vibrometry suggests that this tympanal arrangement provides a novel mechanism for directional sound reception. Some aspects of its vibratory behavior in a sound field will be reported. [Work funded by NINDCD-DC00103 and Hatch NYC-191403.]