1. This paper presents an analysis of the impulse patterns in the tympanal nerve of Metrioptera branckyptera (L) in response to a variety of insect song stimuli in order to determine the relationship of the syllable rate and of intrasyllabic features to the action-potential sequence.
2. Recordings of the proclamation songs of M. brachyptera and Chorthippus parallelus (Zetterstedt) made with a conventional audio-frequency tape-recorder and with a high-frequency tape-recorder have been analysed. The song of M. brachyptera is composed of five syllables/chirp, corresponding to the opening and closing strokes of the tegmina; each syllable consists of twenty-five to forty intrasyllabic spikes which correspond to individual tooth strikes. The main sound energy lies between 15 and 85 kHz centred roughly on 25 and 67 kHz in the closing syllables and on 45 and 65 kHz in the weaker opening syllables.
3. The song of C. parallelus consists of single chirps with loud downstroke syllables and softer upstroke syllables. The main sound energy lies between 7 kHz and 80 kHz, centred on four bands at about 10-15 kHz, 22-25 kHz, 37-40 kHz and 60-70 kHz.
4. Live song, audio-frequency recordings and high-frequency recordings of M. brachyptera song were used as stimuli for the tympanal nerve preparation. The action potentials produced in response to the live or to the high-frequency recording of the song show a high correlation with the intrasyllabic spikes, though not in response to the audio-frequency recording. Inadequate reproduction may therefore be an important potential source of error.
5. By presenting the high-frequency recording through a band-pass filter various degrees of distortion of the song are achieved, and in this way it is shown that the important features of the proclamation song of the species are the intrasyllabic spikes.
6. The action potentials recorded from the tympanal nerve of M. brachyptera in response to the live song, audio-frequency recordings and high-frequency recordings of C. parallelus confirm the importance of the intrasyllabic spikes, and show that no ‘tuning’ of the tympanal organ to the species song occurs.