Abstract

Katydids produce sound by stridulation of the tegmina for signalling and communication. Most katydids are known to sing at ultrasonic frequencies, as compared to crickets. This has drawn interest to investigate the biophysics of ultrasonic sound production and detection, evolution and ecology (including predator–prey interactions) of these katydids. However, most of these studies are based on species from the neotropics, whereas nearly nothing is known about the relatives from another hyper-diverse region, i.e., Southeast Asia. To address this, a concerted effort to document, record and describe the calling songs of Southeast Asian katydids, especially species which calls at ultrasonic frequencies, were conducted. A study spanning over two years (2018 to 2020) in Malay Peninsula (Singapore and Malaysia), Borneo (Brunei Darussalam and Sabah) and the Philippines revealed previously unknown calls of 24 katydid species from four subfamilies. The calling songs of Southeast Asian katydid species are highly diversified in both the time and frequency domains. Call structure can range from isolated syllables (e.g., Holochlora), continuous trills (e.g., Axylus philippinus) to short pulse-trains (e.g., Euanisous teuthroides) and complex echemes (e.g., Conocephalus spp.). 87.5 % of species have ultrasonic peak frequencies and 12.5 % can be considered extreme ultrasonic callers (peak frequency >40 kHz). The call spectrum ranges from tonal (e.g., spectral entropy = 6.8 in Casigneta sp. 2) to resonant (entropy = 8.8 in Conocephalus cognatus). Of the 24 species whose calls are described here, we also imaged and described the sound-producing structures of 18 species. This study provides a preliminary overview of the acoustic diversity of katydids in Southeast Asia and the authors hope to inspire further investigation into the bioacoustics of little-known katydids from Southeast Asia. Amassing a database of calling songs and sound-producing organs from different species can be important to address the taxonomy impediment while advancing our knowledge about the bioacoustics of Southeast Asian katydids.