Functional morphology of bushcricket ears: comparison between two species belonging to the Phaneropterinae and Decticinae (Insecta, Ensifera)

Summary

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 ofPholidoptera griseoaptera (Decticinae) are protected by tympanal covers whereas inLeptophyes punctatissima (Phaneropterinae) the tympana are thicker and fully exposed. The overall auditory sensitivity ofL. punctatissima is lower and the sensitivity maximum of the hearing threshold lies at higher frequencies compared toP. 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 ofL. punctatissima a higher number of scolopidia is distributed in a smaller range than inP. 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.