Male crickets sing to attract females by scraping the blade-like edge of one forewing over a file of teeth on the other forewing. The `clockwork cricket' sound production model suggests that the catch- and-release of the scraper along the toothed file, producing a clock's familiar ticking sound,provides impulses that maintain the vibration of the sound-producing wing regions. Since katydids are closely related to crickets, they might also use the `clockwork cricket' mechanism – but nobody had tested this, until Fernando Montealegre and Andrew Mason came along(p. 1219).
To find out exactly how spiny devils (Panacanthus pallicornis)produce their serenades, Montealegre and Mason used high-speed video to track the movement of the katydids' scrapers over their toothed files. They saw that male spiny devils use the entire file surface, unlike some crickets and katydids. Sticking reflective tape onto the insects' wings, they accurately traced the scrapers' movements as the katydids sang, using a photodiode to catch light reflecting off the tape. They found that, like in crickets, every sound wave corresponds with a tooth impact. In the `clockwork cricket', the file-bearing wing has to vibrate at high amplitude in order to release the scraper from each tooth. But when Montealegre and Mason recorded katydid wing vibrations with a laser vibrometer, they found that the function of katydids'file-bearing wings is damping rather than vibrating at high amplitude;katydids don't use the `clockwork cricket' mechanism.
So how do katydids sing? Examining their tooth files with an electron microscope, Montealegre and Mason noticed that inter-tooth spacing increases along the file. This means that katydids must increase their scraper's velocity as it traverses the file to maintain the same tooth contact rate,which is necessary to produce a pure tone. It seems katydids serenade their ladies by sweeping their wings at a range of speeds.