Structure and evolution of stridulatory mechanisms in New Zealand wetas (Orthoptera : Stenopelmatidae)

Four types of stridulatory mechanisms were found in 35 species (7 genera) of New Zealand wetas (Orthoptera : Stenopelmatidae). These include: (1) tergo-femoral; (2) tergo-tergal; (3) mandbbuao-mandibular; and (4) pleuro-coxal. These fell into 12 groups, based upon shape, density and pattern of tergal and femoral pegs, number of terga bearing pegs and presence of mandibular tusks bearing stridulatory tubercles. The plesiomorphic condition, consisting of spinose peg patches on 3 or more abdominal tergites rubbed by bands of pegs on the femur, is found in Hemiandrus spp. Apomorphically-derived tergal files have arisen separately in 3 other genera. In Hemideina, (2 species groups) well-formed files are very similar among species. In Deinacrida, (4 species groups), the trend is toward file reduction into one or 2 massive tergal ridges, and embellished femoral pegs. In the tusked wetas (2 gen., 2 spp.), one species has a crude file of many broken ridges. Stridulatory structures on mandibular tusks of both New Zealand species are unique, although the tusks appear to have their origin in African stenopelmatids. The plesiomorphic condition appears to have been deployed originally for defense stridulation (inter-specific communication). Additional intea-specific stridulatory communication developed in Hemideina and Deinacrida, using the apomorphic file and peg mechanisms. Here, the stridulation is associated with defense, calling, mating and disturbance behaviors.