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First published online December 26, 2008
Journal of Experimental Biology 212, i-a (2009)
Copyright © 2009 The Company of Biologists Limited
doi: 10.1242/jeb.028183
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CRICKETS SYNCHRONISE WING VIBRATIONS
kathryn{at}biologists.com
When a male cricket wants to attract the ladies, he starts serenading. Positioning the right wing over the left, he opens and closes his wings to produce a finely tuned tone. According to Fernando Montealegre-Z, the insects produce their song by rasping a `file' structure on the upper wing across a `plectrum' structure along the edge of the lower wing, generating vibrations in both wings. But if that is all that the insects do, they couldn't make their distinctive chirrup. Montealegre-Z explains that Henry Bennet-Clark pointed out in 2003 that the insect's wings would, in theory, be vibrating in opposite directions, disrupting the sound's constant and even tone. Crickets must have found a way around this paradox by switching the direction of the vibration in one of the wings so that both wings vibrate in sync, but it wasn't clear how. Having discussed the conundrum with Daniel Robert at a meeting in Toronto in 2006, Robert invited Montealegre-Z to join his lab in Bristol, UK, to see if they could find a switch in the plectrum wing's vibration (p. 257).
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The team decided to try to get a plectrum wing to sing by dragging a file across it. But getting the wings to vibrate in the lab was extremely challenging. Montealegre-Z remembers that he tried to drive the plectrum wing's vibrations with watch gears and other minute spinning file-like structures, but the hard materials destroyed the insect's delicate wings. Then he tried extracting file structures from mature males' wings and attaching them to a wheel spinning above the plectrum, but the files were too rigid. Eventually it occurred to Montealegre-Z to try wing files from recently moulted young males. They were flexible enough to successfully bend and attach to the wheel, but would they set the wing vibrating?
Turning the motor on, Montealegre-Z gradually slowed the spinning wheel to see if it could drive the wing to sing. Amazingly the plectrum wing began making the distinctive cricket chirrup as the wheel reached the speed at which the wings rub against each other.
Having successfully reproduced the plectrum wing's vibrations in the lab, Montealegre-Z teamed up with electronics engineer James Windmill to laser scan and record sound from the plectrum wing to find out how it tuned its vibrations to the file wing's vibrations.
Scanning hundreds of points on the vibrating wing's surface, the team reconstructed the wing's motion on a computer. They could clearly see that when the plectrum region of the wing vibrated downwards, the harp region, which radiates the sound, moved upwards. The sound-emitting harp region was vibrating almost in sync with the file wing, even though the plectrum section was vibrating out of sync. And when the team focused on the anal node region of the wing, where the vibration changed direction, they could see that the direction switch happened along one of the wing veins. The wing always moved downwards on one side of the vein while moving upward on the other side, like a see-saw rocking on its pivot, just as Henry Bennet-Clark had predicted. So crickets have found a clever way of synchronising their wing vibrations to make a loud sound to catch the ladies' attention.
References
Montealegre-Z, F., Windmill, J. F. C., Morris, G. K. and Robert,
D. (2009). Mechanical phase shifters for coherent acoustic
radiation in the stridulating wings of crickets: the plectrum mechanism.
J. Exp. Biol. 212,257
-269.
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