Changes in wing resonance in dried preserved crickets

Abstract

Male crickets sing to attract females for mating. Sound is produced by tegminal stridulation, where one wing bears a plectrum and the other a wing vein modified with cuticular teeth. The carrier frequency (f_c ) of the call is dictated by the wing resonance and the rate of tooth strikes. Therefore, the f_c varies across species due to the size of the vibrating membranes on the wings and/or the speed of tooth strikes. But how well is the resonant frequency (f_o ) conserved in dried preserved specimens? This project is designed to investigate the gradual change in cricket wing f_o over time and aims to produce equations that help to predict or recover the original natural frequency of wing vibration in dry-preserved crickets and allies. Using laser Doppler vibrometry, we scanned the wings of living specimens to determine their f_o . The specimens were then preserved, allowing us to continue measuring the wings f_o as they desiccate. We found that after the first week, f_o increases steeply, reaching a plateau and stabilizing for the following months. We go on to propose a model that can be used to recover the original f_c of the wings of preserved Ensifera that use pure tones for communication. Models were corroborated using preserved specimens previously recorded and mounted in dry collections for more than 10 years.

Keywords: Ensifera; carrier frequency; desiccation; laser Doppler vibrometry; stridulation; wing resonance.

Figure 1.

Gryllus bimaculatus male calling song under laboratory conditions recorded at a temperature of 19°C. (a) A section of the song of G. bimaculatus. (b) Close-up view of a syllable. (c) Power spectrum of a syllable. (d) Spectrogram of a syllable where brighter colours indicate greater acoustic power.

Figure 2.

Macrobinthus jharnae male calling song under laboratory conditions recorded at a temperature of 19°C . (a) A section of the song of Ma. jharnae. (b) Close-up view of a syllable. (c) Power spectrum of a syllable. (d) Spectrogram of a syllable where brighter colours indicate greater acoustic power.

Figure 3.

Microbinthus pintaudi male calling song under laboratory conditions recorded at a temperature of 19°C. (a) A section of the song of Mi. pintaudi. (b) Close-up view of a syllable. (c) Power spectrum of a syllable. (d) Spectrogram of a syllable where brighter colours indicate greater acoustic power.

Figure 4.

The average changes in wing resonance over a four-week period using laser Doppler vibrometry for attached wings. (a, b) The left and right wings of a male G. bimaculatus. (c, d) The left and right wings of male Ma. jharnae. (e, f) The left and right wings of male Mi. pintaudi. LW, left wing; RW, right wing.

Figure 5.

Average wing resonances displayed against calling song carrier frequency for attached wings. (a) The average resonances of the left wings plotted against carrier frequency. (b) The average resonances of the right wings plotted against carrier frequency. f_o, resonant frequency.

Figure 6.

The recovered wing resonances of preserved specimens plotted with carrier frequency. f_o, resonant frequency.

Figure 7.

The change in wing resonance over a four-week period for the attached wings of a single male Macrobinthus jharnae. Power spectra comparing left (blue) and right (red) wing vibrations against calling song (grey) with images of the displayed wings. LW, left wing; RW, right wing.