SIMILAR STRUCTURAL DIMENSIONS IN BUSH-CRICKET AUDITORY ORGANS IN SPITE OF DIFFERENT FORELEG SIZE - CONSEQUENCES FOR AUDITORY TUNING

The bushcricket species Decticus albifrons, Decticus verrucivorus and Pholidoptera griseoaptera (Tettigoniidae) belong to the same subfamily (Decticinae) but differ significantly in body size. In spite of the g reat differences in the dimensions of the forelegs, where the auditory organs are located, the most sensitive range of the hearing threshold lies between 6 and 25 kHz in each case. Only in the frequency range f rom 2 to 5 kHz and above 25 kHz, significant differences are present. The anatomy of the auditory receptor organs was compared quantitativel y, using the techniques of semi-thin sectioning and computer-guided mo rphometry. The overall number of scolopidia and the length of the cris ta acustica differs in the three species, but the relative distributio n of scolopidia along the crista acustica is very similar. Additionall y, the scolopidia and their attachment structures (tectorial membrane, dorsal tracheal wall, cap cells) are of equal size at equivalent rela tive positions along the crista acustica. The results indicate that th e constant relations and dimensions of corresponding structures within the cristae acusticae of the three species are responsible for the si milarities in the tuning of the auditory thresholds.