Triencentrus atrosignatus (Brunner von Wattenwyl, 1895)

(1 male recorded) We successfully recorded the singing of one specimen at 28°C. This male's duty cycle was extremely low: in making a succession of seven call he sang for about 1/3 of 1% of the time available. Each call was a zip lasting 106.7 ms (c.v. = 1.6%). One complete zip is shown in Fig. 31 A. Average down time between calls was 35.8 s (n=9).

The amplitude modulation of the call is complex and a little variable; it incorporates trains of rapid-decay pulses of low amplitude as well as trains of higher amplitude prolonged pulses (Fig. 31B); within the trains these latter tend to increment in duration. The maximum prolonged pulse duration achieved was in the final train (Fig. 31B,C): 2.1 ms.

The call always begins with a pair of low-amplitude rapid-decay pulse pulse trains. Then there are a few short sinusoidal pulses at higher amplitude and finally a short succession of the rather variable (presumed) phonatomes, each comprised of a minor low amplitude train preceding a major train of several maximally sustained pure tone pulses (Fig. 31 A,B).

Though this insect's song includes so many low amplitude rapid-decay pulse trains, its spectrum is is nevertheless dominated by a single relatively high-Q peak of unusual symmetry (Fig. 31 D,E). At any signficant distance from a singer a female would only perceive this dominant carrier. The peak is the product of the higher intensity pulses which involve one dominant frequency: 29.3 kHz (c.v1.3%). Though not obvious in all spectra there are also very low harmonic peaks. There is a fundamental at 14.5 kHz >37 dB down. The principal carrier is thus the first harmonic of this suppressed fundamental. Other low harmonic peaks occur, 2'nd, 3'rd, 5th, all >30 dB below the dominant peak. One prolonged pulse is shown (Fig. 31C) at a resolution that reveals the pure-tone sinusoid; the power spectrum of this particular time sample is shown in Fig. 31 E. [1]

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