Acoustic relationships between tympanate moths and the Hawaiian hoary bat (Lasiurus cinereus semotus)

Abstract

Certain moths possess tympanic organs (ears) that detect the echolocation signals of hunting, insectivorous bats. The auditory characteristics of these ears are matched to the acoustic features of the echolocation calls emitted by the moths' sympatric bat fauna. The two-celled ears of noctuoid moths from the Hawaiian island of Kauai, a site with only one species of bat (Lasiurus cinereus semotus), were electrophysiologically examined to determine their auditory threshold curves. 1. Kauaian moths possess peripherally functional ears with auditory thresholds broadly tuned to 15-55 kHz. Audiograms are intraspecifically stereotyped at these frequencies and thereafter exhibit considerable variability. Threshold variability at both high (>55 kHz) and low (<10 kHz) frequencies may reflect the absence of acoustic selection pressure at these frequencies. 2. Compared to the audiograms of noctuoid moths from a Nearctic site of low bat diversity (Ontario, Canada), Kauaian moths reveal similar sensitivities in the high frequency range (>85 kHz) but are significantly more sensitive to low frequencies (<20 kHz). The similarity in high frequency sensitivity in moths from these two sites is likely due to the common absence of bats echolocating at these frequencies. 3. Compared to noctuoids from a subtropical site of high bat diversity (Zimbabwe, Africa), Kauaian moths reveal reduced sensitivity to most frequencies above 25 kHz, frequencies regularly emitted by the Zimbabwean bat fauna. Kauaian moths, however, possess greater sensitivity to low frequencies (<15 kHz). 4. The noctuid moth, Ascalapha odorata, tested in Kauai and compared to individuals from Panama, a tropical high bat diversity site, shows significant differences which resemble the species-assemblage comparisons (i.e. reduced high frequency sensitivity and increased low frequency sensitivity). 5. Free-flying moths exhibited a variety of evasive flight maneuvres to escape the predatory attacks of L. c. semotus. The auditory characteristics of Kauaian moths suggests that these insects detect both this bat's 9.8 kHz, social call and its 27.9 kHz, echolocation signal. This may represent a case of an insect prey exploiting the social behavior of a predator for its own survival. © 1984 Springer-Verlag.