Polysarcus denticauda (Charpentier, 1825)

The calling song of the male, produced mainly in warm sunshine, is loud, rather complex and highly characteristic. Typically it consists of a prolonged buzz of rapidly repeated syllables (often produced while the male moves through the vegetation) interrupted at lon intervals (often of 1-3 minutes) by a series of loud 'clicks'. The syllable repetiton rate is usually within the range 15-35/s for most of the buzzing phase, but for a few seconds before the clicks are proiduced the rater is increased to about double this value, ranging from 25/s to 70/s or even faster. Oscillographic analysis shows that, during at least the prolonged slower buzz, each syllable is composed of two quite distinct sounds so that it appears to be a diplosyllable. Heller (1988) has shown, however, that both sounds are produced during the closing stroke of the fore wings, the opening stroke being very rapid and silent. This dual structure of the closing hemisyllable often persists during the more rapid buzz that preceds the clicks, but sometimes these more rapidly repeated hemisyllables become almost or copletely uniform bursts of sound. The slow hemisyllables usually last about 20-50 ms and the faster ones about 10-30 ms.

The acceleration in syllab;e repetition rate preceeding the clicks usually begins about 5-10 s before the first click, and generally lasts no more than a second or two until the maximum rate is achieved. Sometimes there is only a single click, but more often there are a series of clicks (often 2-6, but sometimes as many as 20 or more) with the buzzing continuing between them. When there are only a few clicks, they are repeated at ever descreasing intervals (the first interval usually being about 1-2 s); each click is followed by a very brief pause (usually within the range 50-150 ms) and then the high-speed buzzing is resumed until the next click. When there are a large number of clicks, the later ones are generally repeated at a fairly constant rate (often baout 5-7/s), and the buzzing between them becomes reduced to the slower of the two rates or even slower.

After the last click there is sometimes a pause of several seconds before the cycle begins again with a long period of slow-rate buzzing, but more often there is only a very short interval (less than 200 ms) and sometimes, especially if there are a large number of clicks, the buzzing follows immediately after the last click with no pause whatever. Sometimes there is a short period (usually about 1 s) of rapid buzzing after the last click before the syllable repetition rate is reduced to the slower rate.

Heller (1988) has shown that during the buzzing phase the fore wings are vibrated in a relatively open position, and the clicks are produced by the forewings being moved to a much more closed position, each click being a closing hemisyllable using a more proximal part of the file. [1]

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