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The song of the New Zealand weta, Hemideina thoracica (Orthoptera: Stenopelmatidae)
Author(s) -
McVean Alistair
Publication year - 1986
Publication title -
journal of zoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0952-8369
DOI - 10.1111/j.1469-7998.1986.tb01506.x
Subject(s) - stridulation , orthoptera , thoracica , biology , tettigoniidae , anatomy , gryllus bimaculatus , zoology , crustacean , cricket , barnacle
Sound is produced by the New Zealand weta, Hemideina thoracica (White, 1846), by relative movement between a field of pegs situated on the medial surface of the metathoracic legs and a pair of abdominal files on the second abdominal tergite. In defensive stridulation, the metathoracic legs are raised above the body, straightened and rotated downwards. Sound is emitted only on the downward stroke and the pegs and files are orientated to obtain maximal effective contact in this direction only. In intraspecific communication male, but not female, wetas stridulate by reversing the above process: the metathoracic legs are held on the substratum while the abdomen is oscillated up and down. Sound is emitted only on the upstroke. Songs generated by abdominal oscillation contain between one and nine syllables which repeat at about 2.5 Hz. The syllable is about one‐seventh the duration of the intersyllabic interval, but the duration of both increases steadily during the song. The sound spectrum of the song forms a broad, low frequency band, peaking at 3.3 kHz, above which there is a sharp fall off, although there are ultrasonic components present. The structure of the stridulatory structures changes gradually with successive instars. Peg number increases as the weta becomes larger, the pegs become less rounded, the width of the file ridges and space between increase as does the number of potential contacts between the two surfaces generated in one sweep. At all stages there are pegs on the femur which are not reached by the file, while the number of impulses in a syllable are only a small fraction of the number of potential contacts. The ridges on the files are evenly spaced. while the peg distribution is irregular but declines in density distally and ventrally. The sound spectrum of small wetas, produced by imposed stridulation, contains a spectral peak of higher frequency than does that of adult wetas, though the lack of wear on the pegs in all but the larger wetas indicates that. although the structures develop gradually from instar to instar, only the adult and possibly the last instar stridulate. The structure, innervation and contraction rate of proximal limb muscles are those of slow‐ to medium‐speed insect skeletal muscle. The rǒle of abdominal stridulation is discussed.