Signals and Sex-Specific Active Space in a Duetting Insect (Orthoptera: Phaneropteridae: Poecilimon affinis)

Members of the family Phaneropteridae are well known for their acoustical duetting behaviour, used for locating and meeting a mate. In Poecilimonaffinis, typically the male approaches a responding female phonotactically. A set of behavioural experiments, bioacoustic and neurophysiological measurements (some with a relatively low sample size, but not repeatable under the same circumstances) indicates the following system: the male song (92 dB SPLpeak at a distance of 1 m) is about 10 dB louder than the female song. The females respond to male signals only if these are ∼15–20 dB above their hearing threshold. The males start a phonotactic approach towards a stationary, responding female only if she is no more than ∼12 m away. Females, on the other hand, may respond to singing males up to a distance of 28m, and to more distant males with softer signals than to closer ones. A possible function of these weak signals, inaudible for the duetting male, may be to attract eavesdropping males. The communication system will work at densities as low as 0.003 females or 0.0005 males per m2.