D.N.LAPSHIN, D.D. VORONTSOV
ACOUSTIC IRRADIATION PRODUCED BY FLYING MOTHS (LEPIDOPTERA, NOCTUIDAE)
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.