COMMUNICATION BY SUBSTRATUM VIBRATION IN THE NEW-ZEALAND TREE WETA, HEMIDEINA-FEMORATA (STENOPELMATIDAE, ORTHOPTERA)

The propagation of vibrations along the trunk and branches of a manuka tree, generated in response to the impact of a steel ball-bearing on the trunk, was measured with an accelerometer. The impact generated be nding waves which travelled along the trunk and into the branches. Clo se to the point of impact the waveform was dominated by a damped oscil lation at 518 Hz; as the bending wave progressed away from the point o f impact the frequency of the dominant waveform increased. Beyond 200 cm the waveform became increasingly complex and a small-amplitude, hig h-frequency component progressively preceded the main wave. Branching points also induced complex waveforms, particularly where branches lay at a large angle to the trunk. Stridulating wetas also generated bend ing waves in the tree at a frequency close to that generated by the ba ll-bearing, as well as at a higher frequency of 7.5 kHz. The acoustic frequency of stridulation peaked at 0.8 and 3.4 kHz. Records from nerv es serving the vibration-sensitive subgenual organs showed that wetas can detect oscillations at 1 kHz at 0.015 ms(-2). A stridulating weta placed on the same log as a preparation in which the nerve from the su bgenual organ was monitored generated oscillations well above the thre shold for detection.