Date Published: June 5, 2014
Publisher: Public Library of Science
Author(s): Fabio A. Sarria-S, Glenn K. Morris, James F. C. Windmill, Joseph Jackson, Fernando Montealegre-Z, William J. Etges.
This article reports the discovery of a new genus and three species of predaceous katydid (Insecta: Orthoptera) from Colombia and Ecuador in which males produce the highest frequency ultrasonic calling songs so far recorded from an arthropod. Male katydids sing by rubbing their wings together to attract distant females. Their song frequencies usually range from audio (5 kHz) to low ultrasonic (30 kHz). However, males of Supersonus spp. call females at 115 kHz, 125 kHz, and 150 kHz. Exceeding the human hearing range (50 Hz–20 kHz) by an order of magnitude, these insects also emit their ultrasound at unusually elevated sound pressure levels (SPL). In all three species these calls exceed 110 dB SPL rms re 20 µPa (at 15 cm). Males of Supersonus spp. have unusually reduced forewings (<0.5 mm2). Only the right wing radiates appreciable sound, the left bears the file and does not show a particular resonance. In contrast to most katydids, males of Supersonus spp. position and move their wings during sound production so that the concave aspect of the right wing, underlain by the insect dorsum, forms a contained cavity with sharp resonance. The observed high SPL at extreme carrier frequencies can be explained by wing anatomy, a resonant cavity with a membrane, and cuticle deformation.
Various animal taxa use ultrasound (>20 kHz) from bats and cetaceans to insects. They use these shorter wavelengths for orientation and communication with mates and rivals . Among insects, orthopterans are known for calling acoustically with many species sensitive to ultrasound –. Tettigoniidae (katydids) are exceptional Orthoptera in the extent to which they exploit ultrasound. Based on a survey of published sound recordings that address the presence of ultrasound, 70% of katydids call using carrier frequencies (carrier in the sense of the most intense spectral peak) beyond 20 kHz . Only about 5% call below 10 kHz, and 25% between 10 and 19 kHz, , –.
Supersonus is a new genus of neotropical predaceous katydids with at least three species that use extraordinarily high ultrasonic frequencies (>115 kHz) for conspecific communication. Males produce these high-frequency mating calls with unusually high SPL. Typical SPL measures of katydids for microphones positioned at 10–15 cm dorsal to a specimen were 70–100 dB , ,  though a few katydid species have been reported to exceed such output ranges (Table S1). For Supersonus spp., we hypothesize their unusual intensity to be the result of special features integrated into the mechanism of stridulation evolved by these insects: a monopole-like source, wing resonance, and wing deformation occurring under high shear forces. A monopole source radiates equally in all directions. By contrast, a dipole (doublet source) is like two monopoles of equal strength and opposite phase set back to back, alternately radiating sound with maxima normal to one side minima normal to the other , .
A number of species, including those dealt with in the present paper, were erroneously assigned to the genus Arachnoscelis–, mainly because of their shared general appearance, i.e. long and spiny legged and resembling spiders (Fig. 1). Recently Montealegre-Z et al.  redescribed the genus Arachnoscelis, from a particularly abundant population of Arachnoscelis arachnoides, the type species of the genus as originally described by Redtenbacher 1891 . Those authors highlighted the fact that A. arachnoides does not share immediate synapomorphic features with the other species (including some Supersonus spp.) misdescribed within Arachoscelis after the original description by Karny 1911 .