Active auditory mechanics in female black-horned tree crickets (Oecanthus nigricornis)

The acoustic signalling behaviour of many tree cricket species is easily observed and has been well described. Very little is known, however, about the receivers in these communication loops. The exception to this is a single Indian species (Oecanthus henryi) which employs active auditory mechanics to enhance female sensitivity to quiet sounds at male calling frequencies. In most species, male calls have been described, but whether or not sender-receiver matching is present is uncertain. Here we investigate auditory mechanics in females of the North American black-horned tree cricket (Oecanthus nigricornis). The response of the anterior tympanal membrane is nonlinear, exhibiting a lack of tuning at high amplitudes (60 dB and above) but as stimulus amplitude decreases, the membrane becomes tuned to around 4.3 kHz. The tuning of the membrane falls within the frequency range of male calls indicating sender-receiver matching at low amplitudes, which could aid localisation of the highly directional calls of males. The extent of active auditory mechanics in tympanal insects is not yet known, but this paper provides an indication that this may indeed be widespread in at least the Oecanthinae.