Low-frequency vibration transmission and mechanosensory detection in the legs of cave crickets

Vibrational communication is common in insects and often includes signals with prominent frequency components below 200 Hz, but the sensory adaptations for their detection are scarcely investigated. We performed an integrative study of the subgenual organ complex in Troglophilus cave crickets (Orthoptera: Rhaphidophoridae), a mechanosensory system of three scolopidial organs in the proximal tibia, for mechanical, anatomical and physiological aspects revealing matches to low frequency vibration detection. Microcomputed tomography shows that a part of the subgenual organ sensilla and especially the accessory organ posteriorly in this complex are placed closely underneath the cuticle, a position suited to evoke responses to low-frequency vibration via changes in the cuticular strain. Laser-Doppler vibrometry shows that in a narrow low-frequency range the posterior tibial surface reacts stronger to low frequency sinusoidal vibrations than the anterior tibial surface. This finding suggests that the posterior location of sensilla in tight connection to the cuticle, especially in the accessory organ, is adapted to improve detectability of low-frequency vibration signals. By electrophysiological recordings we identify a scolopidial receptor type tuned to 50–300 Hz vibrations, which projects into the central mechanosensory region specialised for processing low-frequency vibratory inputs, and most likely originates from the accessory organ or the posterior subgenual organ. Our findings contribute to understanding of the mechanical and neuronal basis of low-frequency vibration detection in insect legs and their highly differentiated sensory systems. •The accessory organ (AO) is a scolopidial organ in the legs of orthopteroid insects, presumed to detect low frequency vibration signals (< 200 Hz).•In Troglophilus cave crickets, the AO is situated closely underneath the cuticle posteriorly in the proximal tibia.•The mechanical leg response to low-frequency vibration stimuli is stronger at the posterior than at the anterior side of the proximal tibia.•A vibratory receptor neuron was identified in Troglophilus with physiological and anatomical characteristics indicating the origin in the AO.