Fig. 1. (A) Oscillograms of calls recorded from male N. robustus (top trace) and N. bivocatus (bottom trace) at 25°C. The filled arrowheads indicate sound produced during closing movements; open arrowheads represent the sound generated during the opening movements of the tegmina. (B) Durations of the pulses produced during the closing movements of the wings and of the intervals between them (Walker, 1975) in the calls of N. robustus and N. bivocatus (mean ± S.D.; N=12 and 8, respectively). Due to the two alternating pulse periods of N. bivocatus, two combinations of pulse and interval are given for this species; pulse durations were combined with the duration of the following interval. (C) Oscillograms of the models of the conspecific calls of N. robustus (top trace) and N. bivocatus (bottom trace) used in this study. Note the different time scales in A and C.