D.N. LAPSHIN, D.D. VORONTSOV
SOUND SENSITIVITY OF SILKWORM MOTH BOMBYX
Silkworm moths (Bombyx mori L.) being in fixed flight were stimulated with short (2,5 ms) pulses which were presented synchronously with wingbeats. It was shown, that silkworm moths which do not have specialised acoustic organs, nevertheless, are capable to react to sound. Behavioural thresholds faintly depended on filling frequency of the stimulus from 10 to 100 kHz. There is an appreciable decrease of thresholds in the range from 7 to 2 kHz in all audiograms received. Individual threshold values vary from 40 to 80 dB SPL. Trichoid sensillae are offered as probable receivers of sound. Using mathematical modelling it was shown that with a small anisotropy in aerodynamic resistance of sense bristle of trichoid sensilla (about 2-6 %) arising owing to a deviation of its cross section from circular the non-linear effects of transformation of sound fluctuations into vibration become essential. Because of non-linearity of transformation a low-frequency component repeating the form of amplitude envelope of stimulus and independent from it's filling frequency appears. The sensitivity of mechanoreceptors to such slow signals can be rather high. Because of the aerodynamic anisotropy trichoid sensillae should also have directional sensitivity.
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