COMPLEX TIBIAL ORGANS IN THE FORELEGS, MIDLEGS, AND HINDLEGS OF THE BUSH-CRICKET GAMPSOCLEIS-GRATIOSA (TETTIGONIIDAE) - COMPARISON OF THE PHYSIOLOGY OF THE ORGANS

Complex tibial organs are found in all three pairs of legs of tettigoniids and consist of the subgenual organ, the intermediate organ, and the crista acoustica. In the forelegs of most tettigoniids, the tibial organs in association with tympanic membrane, tracheal tube, and spiracle are highly developed sound transmitting structures (tympanal organs), but not so in the mid and hind pairs of legs (tympanal organs). We have studied the electrophysiology of the atympanal organs and in particular of the intermediate organ and the crista acoustica using extracellular recordings to obtain summed responses to vibratory and acoustic stimuli and single cell recordings from the different receptor cells. Significant differences in the responses of the receptor cells of the tympanal and atympanal organs were found predominantly in the case of sound stimulation. Whereas the crista acoustica and the distal part of the intermediate organ of the foreleg are very sensitive auditory receptor organs, the same organs in the mid- and hindlegs appear to respond not at all or only unspecifically to airborne sound stimuli. By contrast, the responses to vibratory stimuli are similar if not identical. The functions of the subgenual organs in all six legs are basically identical, but the function of the middle and distal parts of the crista acoustica in the mid- and hindlegs remains to be characterized. (C) 1994 Wiley-Liss, Inc.