Characterization of auditory afferents in the tiger beetle, Cicindela marutha Dow.

We have identified a nerve carrying auditory afferents and characterized their physiological responses in the tiger beetle, Cicindela marutha. 1. The tympana are located at the lateral margins of the first abdominal tergum. The nerve carrying the tympanal afferents is a branch of the dorsal root from the first abdominal ganglion. 2. Both male and female auditory afferent responses are sharply tuned to 30 kHz with sensitivities of 50-55 dB SPL. 3. The auditory afferents show little adaptation and accurately code the temporal characteristics of the stimulus with the limit of a resolution of 6-10 ms. 4. The difference in threshold between contralateral and ipsilateral afferents for lateral stimuli is greatest at 30 kHz and is at least 10-15 dB. 5. Ablation studies indicate that the floppy membrane in the anterolateral corner of the tympanum is crucial for transduction while the medial portion of the tympanum is less important. 6. The tiger beetle and acridid (locust and grasshopper) ears have evolved independently from homologous peripheral structures. The neural precursor of the tympanal organs in both animals is likely the pleural chordotonal organ of the first abdominal segment.