Are all auditory sensilla of bushcrickets bimodal? Comment on: R. D. Zhantiev and O. S. Korsunovskaya, Functions of chordotonal sensilla in bushcrickets (Orthoptera, Tettigoniidae); Entomological Review, 2021, vol. 101 (6), pp. 755–766

Abstract

Detection of sound and substrate vibration is crucial for the survival and reproduction of many animals, particularly insects. Bushcrickets (Orthoptera, Tettigoniidae), developed a large mechanosensory organ complex in their legs to detect such stimuli. As demonstrated by various studies in the past, sensilla in distinct functional groups form specialized vibratory organs (the subgenual organ and the accessory organ), respond sensitively to both vibration and sound (in the intermediate organ [IO]), or mediate hearing (in the crista acustica [CA]; the tympanal hearing organ). In their recent publication, Zhantiev and Korsunovskaya addressed auditory and vibratory sensitivity in the IO and the CA in two species of bushcrickets, using single-cell recording and staining of sensory neurons from their soma in an isolated foreleg. Their main finding was that not only the IO but also the complete CA contains bimodal sensilla responding with high sensitivity to both sound and vibration, which would be a true change in the paradigm of how the auditory/vibratory sense in Orthoptera works. In addition, they revealed vibratory tuning of the IO sensilla, which differs largely from that in previous studies. We propose three major experimental causes of such discrepancies: calibration, experiments with isolated legs, and differences in the sites of recording. To judge the causes of these discrepancies more adequately, a detailed comparison of methods and a number of control experiments are needed. This will deepen our understanding of sensory adaptations and specialization of insect mechanosensory organs to stimuli entering the system by different input pathways.

Bimodality of auditory receptors in bush‐crickets. Сontinued discussion. It's time to experiment

“…Our paper on the bimodality of auditory receptors in bush‐crickets (Zhantiev & Korsunovskaya, 2021) elicited a comment published by Drs N. Stritih‐Peljhan, J. Strauß, and A. Stumpner (Stritih‐Peljhan et al, 2022). When registering the activity of individual receptors directly in the tympanal organ, we have found that they perceive vibrations along with sound stimuli.…”

“…At this stage, the registration was extracellular. In this case, responses to both sound and vibrations were recorded without the possible (Stritih‐Peljhan et al, 2022) influence of the microelectrode on receptor activity. Further lowering of the electrode could lead either to entry into the tympanal nerve (Figure 2a,1), or penetration into the receptor soma or to intracellular registration in the receptor axon (Figure 2a, 2b) or dendrite.…”