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CRICKET'S WINGS DOUBLE UP
kathryn{at}biologists.com
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Like a violin player that picks up their instrument with the left hand, the Australian cricket always closes the right wing over the left when it begins to call. The insect begins with a chirrup, followed by a train of trilling notes as it makes successive wing movements and draws a plectrum on the upper side of the left wing along a serrated file structure on the bottom of the right. Henry Bennet-Clark is fascinated by the loud sounds that these tiny insects make, so he began analysing how the crickets produce their distinctive call.
First he tested the wings' acoustics, and discovered that a system of veins in the wing begins resonating as the insect pushes the plectrum over the upper wing's file. This was unexpected, as the harp membrane that lies between the resonating veins had been thought to be the main resonant structure, but it seems that it simply helps to radiate the sound.
He also tested each wing's resonance to see whether the low pitched Australian cricket sang like its higher pitched bush cricket relatives; a bush cricket's file wing remains silent when it begins chirruping. When he analysed the Australian cricket's wings' resonances he found that the left wing's resonant frequency was at the same pitch as the insect's song, but the right wing's resonant frequency was much lower than the left's. However when the right wing was played by driving the stiff plectrum along the file, the right wing's pitch rose, to match the left wing. So when the cricket sings, both wings vibrate at the same frequency. Bennet-Clark explains that the low pitched Australian crickets are `under selection pressure to maximise the size of the [sound] source and achieve this by using both wings'.
References
Bennet-Clark, H. C. (2003). Wing resonances in
the Australian field cricket Teleogryllus oceanicus. J. Exp.
Biol. 206,1479
-1496.
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