Acoustic and vibrational signaling in true katydid Nesoecia nigrispina: three means of sound production in one species

Abstract

The males of Mexican katydids Nesoecia nigrispina (Stal, 1873) produce calling songs and protest sounds using the typical stridulatory apparatus, situated, as in most of the other Ensifera, at the bases of the tegmina. It includes a stridulatory file on the upper tegmen and a plectrum on the lower one. The calling sounds, which are of two types (fast and slow), are two-syllabic series, with a repetition rate fluctuate within 3–4.5 s−1 (fast) and 1.2–2 s−1 (slow). After tactile stimulation, males produce protest signals in the form of short trills of uniform syllable duration. The syllable repetition rate is higher than that of the calling sounds: 7.7 s−1. The frequency spectra of these signals have maxima in the band of 14–15 kHz. However, in addition to the sounds described, both males and females are capable of producing protest signals of the second type, with the help of another sound apparatus, namely the hind wings. Apparently, the sound is produced by the friction of the hind wings on the lower tegmen. The dominant frequencies in the frequency spectra of these sounds are 40–60 kHz. In adults of both sexes and older nymphs, in response mainly to tactile stimulation, short clicks are recorded, which they produce, apparently, by the mandibles. Thus, N. nigrispina seems to have the most extensive acoustic repertoire among pseudophyllines and three means of emitting sound signals. Tremulatory substrate-borne vibrations are produced by individuals of both sexes during courtship and by males completing the calling signal cycle and after copulation. It is possible that vibrational signals are an additional factor in the reproductive isolation of sympatric species, since the calling sound signals in representatives of the genus Nesoecia are similar and exhibit considerable variability. The type and parameters of the calling signal used by the female during recognizing a conspecific mate remain unclear.