Acoustic behaviour as a generic character in New Zealand cicadas (Hemiptera: Homoptera)

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Abstract
Pulse patterns of certain New Zealand Cicadidae (Subfamily Tibicininae) represent hitherto undescribed modes of increasing the repetition rate of clicks in tymbal song. Elaboration of tymbal song by addition of wing-clapping is characteristic of the genus Amphipsalta Fleming, but subdued wing-clapping is also observed in Kikihia Dugdale and Notopsalta Dugdale, not however as a regular element in the song. Rhodopsalta Dugdale and Maoricicada Dugdale differ from the other genera in lacking an alarm note. In Kikihia and Maoricicada, in-out doublet pulses result from the buckling of the two tymbals, generally in unison, but the click repetition rate is lower in Kikihia than in most Maoricicada. In most species of Maoricicada pulses are regularly repeated to generate long notes with regular intervals between clicks but in others the intervals between clicks may be gradually or abruptly altered; in one species the repetition rate is increased by alternation of doublets from right and left tymbals and in another decreased by suppression of the out click. In Rhodopsalta in-out doublets from the two tymbals are of unequal length, so as to produce triplet pulse groups. In Amphipsalta the tymbal buckles inwards in two stages as its muscle contracts, giving two clicks, but pops out with a single click, so that each tymbal produces a triplet pulse group. The muscles contract alternately so that the last click of the tymbal from one side generally coincides with the first click from the other, producing a quintuplet pulse group, in which the middle signal has greater amplitude than others. In Notopsalta the normal pulse group is a rapid quadruplet produced by the alternating clicks from left and right tymbals, but one of the tymbals sometimes buckles outwards in two stages to complicate the pulse group and further increase the click repetition rate. This facultative two-stage buckling perhaps represents a stage in the evolution of the obligate two-stage buckling characteristic of Amphipsalta. Thus, the structure of the pulse groups that make up the tymbal song of New Zealand cicadas is characteristic for each of the 5 groups of species distinguished as genera by Dugdale in 1972, so that mechanism of sound production is to some extent correlated with taxonomic classification.

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