CHARACTERIZATION OF AUDITORY AFFERENTS IN THE TIGER BEETLE, CICINDELA-MARUTHA DOW

We have identified a nerve carrying auditory afferents and characteriz ed their physiological responses in the tiger beetle, Cicindela maruth a. 1. The tympana are located at the lateral margins of the first abdo minal tergum. The nerve carrying the tympanal afferents is a branch of the dorsal root from the first abdominal ganglion. 2. Both male and f emale auditory afferent responses are sharply tuned to 30 kHz with sen sitivities of 50-55 dB SPL. 3. The auditory afferents show little adap tation and accurately code the temporal characteristics of the stimulu s with the limit of a resolution of 6-10 ms.4. The difference in thres hold between contralateral and ipsilateral afferents for lateral stimu li 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 t ympanum is less important. 6. The tiger beetle and acridid (locust and grasshopper) ears have evolved independently from homologous peripher al structures. The neural precursor of the tympanal organs in both ani mals is likely the pleural chordotonal organ of the first abdominal se gment.