This study presents the first detailed description of the oscillographic structure and spectrographic features of sound emission produced by Z- and E-strain males of Ostrinia nubilalis during their courtship behaviour. Males simultaneously produce ultrasonic and low-frequency sonic sound emissions during their courtship, vibrating their wings at a distance of 1-2 cm from the female. The sound emission shows two characteristic types: a long courtship song is followed by a short precopulation song after a few seconds of silence. The ultrasonic courtship song is composed of pulses repeated in pairs or more typically in long series with an even repetition rate (which showed to be temperature dependent) or in irregular sequences. The precopulation song is a short crescending pulse-series. In both song types the ultrasonic carrier-wave has constant frequency spectrum containing components from 20 kHz to 80 kHz. The low-frequency sound emission has a harmonic frequency spectrum (fundamental frequency between 40-70 Hz). During the precopulation song the low-frequency component shows a characteristic frequency sweep from 80-100 Hz to 70-80 Hz. No significant difference has been noticed comparing the songs of Z- and E-strain males of O. nubilalis. However sound emission is clearly different from that described recently in the closely related O. furnacalis, where pulses are performed in groups forming chirps and no different courtship song and precopulation song has been described. The possible signal function of low-frequency near field sound emission is discussed.
acoustic communication, near field sound, silent signalling, signal species specificity