D.D. VORONTSOV and D.N. LAPSHIN

FREQUENCY TUNING OF THE AUDITORY SYSTEM OF ACOUSTICALLY ACTIVE NOCTUIDS (NOCTUIDAE, LEPIDOPTERA)

We investigated the frequency threshold curves (audiograms) depending on the delay between moths own click and the following short (2.5 ms) tonal stimulus. An insect was considered to respond to the stimulus if the mean spacing frequency of the its own clicks was substantially increased. Moths (Enargia paleacea Esp.) were tested under the tethered-flight conditions. At a delay of 1 ms the minimal thresholds were observed in the frequency range from 40 to 50 kHz, whereas increasing of stimulus delay to 15 ms caused the sensitivity optimum to shift down to 25 kHz. This shift of the sensitivity optimum can be explained supposing that there exists dynamic readjustment of the tympanic membrane mechanical resonance caused by longitudinal tension of the membrane towards the conjunctiva. The moth's ability of quickly tuning the tympanic organs allows it to analyze the spectra of sufficiently long sounds (sequential frequency analysis).

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An example of response

Audiograms

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