Characteristics of acoustic waves accompanying the flight of noctuid moths (Noctuidae) were measured. The low-frequency part of the spectrum is formed of a series of up to 17 harmonics of the wingbeat frequency (30-50 Hz) with a general tendency toward the decrease in the spectral density and the increase in the sound frequency. The root-mean-square level of the sound pressure from flapping wings was found to be 70-78 dB SPL. Besides low-frequency components, the flight of moths was accompanied by short ultrasonic pulses, which appeared with every wingbeat. Most of the spectral energy was concentrated within a range of 7-150 kHz with the main peaks at 60-110 kHz. The short-term pulses were divided into two or more subpulses with different spectra. The high-frequency pulses were produced at two phases of the wingbeat cycle: during the pronation of the wings at the highest point and at the beginning of their upward movement from the lowest point. In most of the specimens tested, the peak amplitude of sounds varied from 55 to 65 dB SPL at a distance of 6 cm from the insect body. However, in nine noctuid species, no high-frequency acoustic components were recorded. In these experiments, the acoustic flow from the flying moth within a frequency range of 2 to 20 kHz did not exceed the self-noise level of the microphone amplifier (RMS 18 dB SPL). Probable mechanisms of the high frequency acoustic emission during flight, the effect of these sounds on the auditory sensitivity of moths, and the possibility of their self-revealing to insectivorous bats are discussed. In addition, spectral characteristics of the moth echolocation clicks were more precisely determined within the higher frequency range (>100 kHz).
Original Russian Text: D.N. Lapshin, D.D. Vorontsov, 2007, published in Zoologicheskii Zhurnal, 2007, Vol. 86, No. 12, pp. 1452-1463.