Is significant acoustic energy found in the audible and ultrasonic harmonics in cricket calling songs?

Abstract

Crickets are known to be inefficient sound producers. When calling, typically less than 1% of their metabolic energy is converted into sound. This low efficiency has been attributed to losses within the insect and to poor acoustic coupling with the environment. A previously uninvestigated factor that might contribute to low efficiency is ultrasonic radiation. If the impacts of the plectrum and file teeth excite vibration in the ultrasonic range, then the sound pressure level meters typically used to measure acoustic power would not accurately detect it. We made audible and ultrasound recordings of the calling songs of a phylogenetically diverse group of 6 cricket species, and, for comparison, 2 katydid species. In most of the cricket species, energy was present well into the ultrasonic region as a series of harmonics of the carrier frequency. However, the energy in these peaks was very small in comparison to the audible-range harmonics. There was no evidence of significant oscillations that were not harmonics of the carrier frequency. In all but one cricket species, over 97% of the total audible and ultrasonic energy was contained in the carrier frequency band.