ACOUSTIC TRANSMISSION CHARACTERISTICS OF THE TYMPANAL TRACHEAS OF BUSH-CRICKETS (TETTIGONIIDAE) .2. COMPARATIVE-STUDIES OF THE TRACHEAS OF 7 SPECIES

The transmission characteristics of the acoustic tracheae in the forel egs of seven tettigoniid species were investigated by sinusoidal analy sis. The species were selected to represent a range of body sizes and leg lengths. Four subfamilies were included, with two species each fro m three of them; the tracheae in such closely related pairs could be e xpected to be similar in shape despite their different dimensions. The tracheae were dissected out for morphometric analysis and compared wi th one another with respect to their overall dimensions and those of t ypical subsections. The amplitude-versus-frequency response of acousti c transmission in the tracheae was measured at various positions with a probe microphone. The stimuli were continuous sinusoidal signals at an intensity of 100 or 110 dB SPL. The tracheae of all the species stu died here (in males and females) are distinguished by a bandpass-limit ed transmission characteristic. In the frequency range above 5 kHz (at least to 40 kHz) the sound signals are amplified by 10-15 dB during p assage through the tracheae. These results are compared with the thres hold curves of the auditory organs and the spectra of the conspecific songs. Although in some cases there are considerable differences in th e dimensions of the tracheae, the transmission characteristics are ver y similar; no specific adaptations to the frequency composition of the conspecific song were found.