The responses of central acoustic and vibratory interneurones in bushcrickets and locusts to ultrasonic stimulation

Abstract

ABSTRACT. Analysis of the ultrasonic content of the calling songs of two tettigoniids, Decticus verrucivorus L. and Tettigonia cantans Fuessly, showed that the major secondary energy peaks in the ultrasonic range are only about 15–20 dB below the main audible frequency peaks. The song of the acridid, Locusta migratoria L., contains no appreciable secondary peaks at ultrasonic frequencies, Bifunctional acoustic‐vibratory interneurones are present in the ventral nerve cord of all three species. They are divided into three categories, according to their response characteristics: VS (vibration and sound), S (sound) and V (vibration) neurones. All the unit‐types capable of coding sound signals in the ventral cord (VS and S neurones) are sensitive to frequencies of up to 100 kHz, with one exception (S3). In tettigoniids, three of these unit‐types are more sensitive at ultrasonic frequencies than they are at the audible frequencies of their conspecific songs. Among the vibratory neurones (V), one unit‐type receives inhibitory inputs from ultrasonic acoustic primary receptors. The possible importance of ultrasonic perception in the natural environment is briefly discussed.