In contrast, no significant difference in hearing was found among the three species with regard to the most sensitive frequencies and hearing threshold levels.
Most sensitive frequencies and threshold sound pressures at the most sensitive frequencies were obtained from individual hearing curves, and then the values were compared among both sexes of four different populations of O. nubilalis [Z type (Darmstadt) and E type (Paris)] and O. scapulalis [Z type (Matsudo) and E type (Matsudo)].
No significant difference between the sexes was found in the most sensitive frequencies (LR test in GLM, quasi error with log link, F1,19 = 3.9, P = 0.050) or in the thresholds at these frequencies (F1,19 = 2.5, P = 0.12).
Thus, the hearing threshold levels at the most sensitive frequencies (42.6±3.5 dB SPL) were significantly lower than the levels of pulse 1 (LR test adjusted with a false discovery rate [26] in GLM, quasi error with log link, F1,58 = 12.20, P = 0.0018) and marginally lower than those of pulse 2 (F1,58 = 2.2, P = 0.13).
No significant difference was found in the most sensitive frequencies and their threshold levels among the species or pheromone types (frequency: F2,22 = 0.2, P = 0.75; mean ± SD = 45.7±9.5 kHz, threshold: F2,22 = 0.9, P = 0.40; 42.6±3.5 dB SPL).
Comparisons between audiograms and sound spectra revealed that the most sensitive frequencies correlate with the dominant frequencies of stridulation sounds in all S. schoutedeni size groups and that all specimens are able to detect sounds of all size groups.
To improve the sensitivity tenfold around the most sensitive frequency region at 100 Hz with respect to first generation instruments, several new techniques are being implemented.
Kenyon [ 15] observed a considerable 60 dB increase in hearing sensitivity in the bicolor damselfish Stegastes (syn. Pomacentrus) partitus at the most sensitive frequency (500 Hz) during ontogeny.
We should note that the human perceptual threshold to vibrotactile stimulation [33, 34] is approximately 10−7 m at the most sensitive frequency.
Thus, the sensitivity study helps the quality control man as well as the manufacturer of such supports to estimate the permissible deviation in the most sensitive frequency zones.
In groups with a fully developed chain of ossicles (S – XL) the most sensitive frequency decreased with size from 4 kHz in groups S and M, to 3 kHz in group L and to 1 kHz in group XL.
