Abstract
The song of Metrioptera sphagnorum (F. Walker) is a prolonged trill alternating regularly between two intensities. Oscilloscope analyses reveal two stridulation modes corresponding to the two intensity levels. These two modes are described in terms of pulse structure.Characteristic frequency spectrograms are associated with each mode. In one mode audio frequencies are emphasized; the other mode is dominated by high intensity ultrasonic frequencies. At the approach of a conspecific male, singers were observed to prolong the audio-dominated stridulation mode.