Ultrasound production by genital stridulation in Syntonarcha iriastis (Lepidoptera: Pyralidae): long-distance signalling by male moths?

Abstract

Males of the pyralid moth, Syntonarcha iriastis Meyrick, perch on vegetation at the tops of trees and bushes and produce ultrasound while their wings are spread and while sclerites at the end of the abdomen are spread to expose the genitalia. Exposing the genitalia appears to engage the sound-producing mechanism; the male genitalia and eighth abdominal sternite of this species are greatly modified and include a file and scraper and possible resonating areas. Sounds produced are consistent between individuals and comprise pulses which are narrow in frequency range, the first pulse being at about 42 kHz and two following pulses at about 57 kHz. The signal is detectable with an ultrasound ‘bat’ detector from 20 m. Two tettigoniid species (Orthoptera) at the same site produced ultrasonic calls of similar frequencies at the same times as the moth; differences in time-amplitude patterns could be used by orienting moths to recognize conspecifics. Signalling by male S. iriastis is compared with that of other pyralid species in which females are attracted to signalling males. The behaviour of S. iriastis males differs from that of other pyralids in that they do not signal in groups or from a resource attractive to females, and do not possess glands known to produce a ‘calling’ pheromone. It is suggested, because of these differences, that sound production in this species does not function at close range, as argued for the wax moth Achroia grisella (Fabricius), but instead as a long-distance calling signal.