SOUND PRODUCTION AND SOUND EMISSION IN SEVEN SPECIES OF EUROPEAN TETTIGONIIDS. PART II. WING MORPHOLOGY AND THE FREQUENCY CONTENT OF THE SONG

ABSTRACT

Sound production in seven species of bush crickets (Tettigonia cantans, T. virridissima, Decticus verrucivorus, D. albifrons, Psorodonotus illyricus, Ephippiger ephippiger, E. discoidalis) has been investigated. Aspects of wing morphology have been compared and show that areas of the dorsal fields and the mirror are correlated with the dominant frequencies of the songs. Tooth removal from the pars stridens produces gaps in the time structure of single syllables but no change in the song power spectra. The removal of the tegminal lateral field in long- and medium-sized wing species (T.c., T.v., D.a., D.v.) produces an increase in the ultrasonic components of caudally-emitted sound. This suggests an absorbing function for the lateral fields in intact animals. In all species removal of a small portion of the mirror frame or of the mirror membrane attenuates the whole stridulatory signal, but especially the ultrasonic components. The mirror therefore functions as an amplifier, especially for high frequencies. Manipulation of the dorsal fields of long- and medium-winged species, or the distal edges of tegmina of brachypterous species, deletes or shifts the songs' dominant frequency. Thus the different tegminal structures (and especially the dorsal fields) contribute to the time structures and power spectra of the stridulatory songs of these species.