FUNCTIONAL-MORPHOLOGY OF BUSH-CRICKET EARS - COMPARISON BETWEEN 2 SPECIES BELONGING TO THE PHANEROPTERINAE AND DECTICINAE (INSECTA, ENSIFERA)

The morphology of the complex tibial organs in the forelegs of two bushcricket species belonging to the Phaneropterinae and Decticinae (Tettigoniidae) is described comparatively. In both species the tibial organs are made up of the subgenual organ, the intermediate organ and the crista acustica; the latter are parts of the tympanal organs and serve as auditory receptors. The very thin tympana in the forelegs of Pholidoptera griseoaptera (Decticinae) are protected by tympanal covers whereas in Leptophyes punctatissima (Phaneropterinae) the tympana are thicker and fully exposed. The overall auditory sensitivity of L. punctatissima is lower and the sensitivity maximum of the hearing threshold lies at higher frequencies compared to P. griseoaptera. The number of scolopidia in the three scolopale organs and the dimensions of parts of the sound conducting system differs in the two species. In the crista acustica of L. punctatissima a higher number of scolopidia is distributed in a smaller range than in P. griseoaptera; the scolopidia are especially concentrated in the distal part. Morphometrical analyses indicate that the dimensions of the spiracles, the acoustic trachea and the tympana determine the overall auditory sensitivity and that the arrangement of the scolopidia and the dimensions of structures in the crista acustica affect the frequency tuning of the hearing threshold.