SEX-SPECIFIC DIFFERENCES IN SONG FREQUENCY AND TUNING OF THE EARS IN SOME DUETTING BUSH-CRICKETS (ORTHOPTERA, TETTIGONIOIDEA, PHANEROPTERIDAE)

Males and females of Holochlora nigrotympana and Stictophaula ocellata engage in acoustical duetting in order to find mates. In these specie s the stridulatory organs and stridulatory movements differ between th e sexes and are not homologous to each other. The spectra of male and female differ slightly in Stictophaula ocellata (peak frequency male 2 7 kHz, female 19 kHz) but distinctly in Holochlora (male 39 kHz, femal e 12 kHz). Measurements of auditory thresholds by recording from the t ympanic nerve show that males are more sensitive than females, probabl y due to larger auditory spiracles, and that male hearing is tuned to female signal. Female sensitivity in Holochlora, however, does not mat ch male song. From comparisons with other cases of auditory mismatch a nd from the typical shape of auditory threshold curves in bushcrickets it can be assumed that tuning of the hearing threshold is restricted by the design of the auditory system.