Involvement of Mechanosensory Complex Structures of the Cricket Gryllus bimaculatus Larvae (Orthoptera, Gryllidae) in Triggering of Motor Responses to Sound

Abstract

Using an ethological approach, we studied the possibility of sound perception as well as probable contribution of diverse mechanosensory systems composing the mechanosensory complex to triggering of motor responses to sound stimulation in the cricket Gryllus bimaculatus larvae. It was shown that larvae can perceive sounds and respond to them by a locomotor reaction in a relatively broad frequency range, which becomes narrower as sound intensity decreases [0.1–6.6 kHz (111 ± 3 dB SPL), 0.1–1.4 kHz (101 ± 3 dB SPL), 0.1–0.8 kHz (91 ± 3 dB SPL]. Sound perception and triggering of motor responses appear to involve the cercal organs (CO), subgenual organs (SO) and, probably, other distant mechanosensory organs (DMO). Normal functioning of CO is essential for triggering locomotor responses to sound within the ranges of 1–1.4 kHz (101 ± 3 dB SPL) and 0.1–0.8 kHz (91 ± 3 dB SPL). CO are not necessary for triggering of motor responses to cues with an intensity of 111 ± 3 dB. SO and, probably, other DMO provide locomotor responses to sound within the ranges of 0.1–6.6 kHz (111 ± 3 dB SPL), 0.1–0.9 kHz (101 ± 3 dB SPL), and 0.1–0.3 kHz (91 ± 3 dB SPL). Thus, last instar larvae of G. bimaculatus lacking the tympanal organs can perceive sounds using CO, SO and, probably, other DMO, which (as in cricket imagoes) are likely to compose an integrated mechanosensory complex providing adequate acoustic behavior of this cricket species. Performance efficiency and sensitivity of the mechanosensory complex (specifically, CO) rely on the thoroughness of grooming. After self-cleaning of CO, the level of larval motor activity in response to cue presentation returned to the baseline and sometimes even increased. We assume that under normal conditions the mechanosensory complex, which triggers motor responses to a sound, is involved in the defensive escape response aimed at rescuing from predators.