Behavioural displays, acoustic and chemosensory communication in the Middle Island tusked weta, Motuweta isolata (Orthoptera: Anostostomatidae)

Abstract

Three methods of communication were examined in the Middle Island tusked weta, Motuweta isolata (Orthoptera: Anostostomatidae); defence behaviour, acoustic and chemosensory signalling. Previous studies had been limited to basic autecology and anecdotal evidence. This study was undertaken to understand the behaviours of this species to assist in conservation efforts. Defensive behaviours were elicited through repeated stimulation while aggressive behaviours were acquired through male-male battles. Femoro-abdominal stridulation was induced within both situations. Defensive stridulation functioned as alarm behaviour and was often accompanied by a visual display. Agonistic stridulation was executed by the eventual winner of combat. Aggressive battles were a progression of behavioural units of increasing risk on injury until an individual was determined the winner. Acoustic analysis was preformed on stridulations observed in aggressive and defensive behaviours. Stridulation was a broad band signal covering a range well above 16 kHz and possibly into the ultrasound range (>20 kHz). Two different forms of stridulation were identified; click train sound and hiss sound. High speed frame-by-frame analysis of stridulation and scanning electron micrographs of the abdomen and medial femur deciphered the mechanism and found the interaction of the cuticle to be unique among weta. Strikingly, micrographs also revealed two morphologies of abdominal projections; truncated ridges and columnar pegs. Both these points were not previously observed. Y-maze and partition tests were utilized for evidence of chemosensory signalling, while gas chromatography-mass spectrometry identified faecal volatiles in M. iisolata and 4 other weta species in a parallel study. Through partition experiments, evidence exists for a species-specific volatile pheromone and a sex-specific chemo-tactile pheromone. Dimethylsulphide, (CH3)2S, was present in the faeces of all 5 weta species, and may be produced by the individual.