CENTRAL NERVOUS CONTROL OF HINDLEG COORDINATION IN STRIDULATING GRASSHOPPERS

Stridulation in many gomphocerine grasshoppers is characterized by spe cific phase shifts between the two hindlegs as well as different movem ent patterns produced by the left and the right leg. The underlying ne uronal excitation patterns are generated by networks on either side of the metathoracic ganglion. The role of the intraganglionic commissure s in right-left coordination and the production of differing movement patterns was investigated by transecting the metathoracic ganglion med iosagittally in Omocestus viridulus, Chorthippus biguttulus and Chorth ippus mollis. In all three species, after this operation both hindlegs produced the same pattern and no longer different movements. The effe cts of transection on coordination differed: rapid movement rhythms, l ike those typical of Ch. biguttulus and the vibratory parts of the son g of Ch. mollis, on the two sides drifted with respect to one another. In contrast, the slow rhythms characteristic of O. viridulus and the song subunits of Ch. mollis were completely synchronized. It is inferr ed that in intact animals the pathways for coordination of the rapid s tridulatory rhythms are exclusively intraganglionic, whereas the phase relations of the slow rhythms are additionally influenced by way of a nterior right-left connections, perhaps within the suboesophageal gang lion.