The effect of tympanal position on the sound-sensitivity of the metathoracic scolopale organ of Corixa

Action potentials were recorded extracellularly from the receptor unit B2 of the metathoracic scolopale organ of Corixa punctata Ill. (Heteroptera, Corixidae). The background discharge rate is modulated by movement of the tympanal membrane, which under normal resting conditions is rhythmically pushed outward (strong excitation) and pulled inward (weak excitation).The receptor unit gives phasic-tonic responses to airborne sound. Threshold curves and intensity characteristics indicate that the sensitivity to sound depends on the position of the membrane at the time of stimulation. The thresholds to frequencies in the range 0.3–3.0 kHz measured with the membrane everted are as much as 20 dB lower than when it is inverted. In the frequency range where sensitivity is greatest (0.3–1.1 kHz), with membrane everted the threshold is ca. 74 dB RMS re 20 μPa.