Unusual mechanism of emission of vibratory signals in pygmy grasshoppers Tetrix tenuicornis (Sahlberg, 1891) (Orthoptera: Tetrigidae).

Acoustic communication plays an important role in the life of insects and especially in representatives of the order Orthoptera. Their vibrational signalling, unlike signalling by sound, is poorly studied. The pygmy grasshoppers Tetrix tenuicornis (Sahlberg, 1891) belonging to the ancestral family Tetrigidae (Orthoptera) can produce several types of substrate-borne vibratory signals using their mid-legs. The emission of these signals is not accompanied by visible movements of any parts of the body. The goal of our study was to elucidate the mechanism of production of these vibrations. For this, we synchronously recorded the vibratory signals and the muscle activity in various regions of the legs and thorax in freely moving males. The obtained results revealed an unusual mechanism for the emission of acoustic signals. We found that the strongest muscle activity during the emission of the vibratory signals was recorded in the mesofemur and mesotibia. According to the position of the electrode, these muscles are the flexor and extensor of the tibia, levators and depressors of the tarsus, and probably pretarsus. The motor system employed during the emission of vibratory signals was most similar to that of the jump of locusts and probably is performed as a result of co-contraction of antagonistic muscles of the tibia, tarsus, and pretarsus. The data obtained make significant additions to the presentation of a variety of insect acoustic communication systems.