Descending stridulatory interneurons in the suboesophageal ganglion of two grasshopper species

Abstract

1. The influences of four types of neurons in the suboesophageal ganglion on stridulation in the acridid grasshoppers Omocestus viridulus (L.) and Chorthippus mollis (Charp.) were investigated by hyper- or depolarizing the neurons during stridulation and recording the stridulatory movements. 2. Suppression of the neuronal activity was never observed to affect the stridulatory movements, whereas an increase in the discharge rate always did so. 3. In both species, depolarization of three of the four types produced a reduction in stridulation amplitude by an amount dependent on the neuronal activity; with sufficiently high discharge rates, stridulation was terminated completely. The period of the song-unit cycle could also be altered, but not the coordination of the associated movements. 4. In Ch. Mollis depolarization for a time shorter than the duration of the song unit resulted in the stridulatory rhythm being reset. 5. Brief depolarization of neurons of type 4 elicited jerky leg movements in the resting animal. When the discharge rate was increased during stridulation, in O. Viridulus the result was a general increase in stridulation amplitude and in Ch. Mollis, a change from the courtship to the rivalry song pattern.