We auditory evoked response (AER) technique an electrophysiological far-field recording method widely used in evaluating vertebrate hearing, was adopted to butterflies to overcome limitations of behavioural and invasive electrophysiological techniques. Response to tone bursts of different frequencies (250 Hz - 15 kHz) and amplitudes was recorded from the surface of the thorax of Erebia pronoe, E. aethiops and E. medusa (Lepidoptera: Satmidae). AER-waveforms of all three species consisted of 2-3 positive peaks. The polarity of these traces was not affected when switching the phase of the sound stimulus by 180°. Latencies of AERS increased with decreasing sound pressure level and frequencies. Perforation of the tympana at the base of the forewings totally eliminated AERS at all frequencies, demonstrating that the recorded potentials were generated solely within the auditory pathway in response to acoustical stimuli. Decapitation did not reduce the number of peaks and amplitude of AER traces, indicating that auditory evoked potentials are generated entirely within the thorax. AER audiograms revealed best auditory sensitivity between 2 and 4 kHz in E. pronoe and E. aethiops, with lowest thresholds at 36 and 31 dB SPL, respectively. These data demonstrate that the AER recording technique is a useful method for measuring hearing in insects when rapid measurements of a large number of species or when repeated testing of animals are required (e.g. during ontogenetic studies). This research was supported by the Austrian Science Fund (FWF grant No 12411 to F.L.) and by the Slovenian Science Foundation (SZF-fellowship to D.R.).
Darja Ribaric & Friedrich Ladich (2002). Auditory evoked responses in insects: a non-invasive method for measuring hearing sensitivity in butterflies [abstract]. Bioacoustics 13(2): 199