Confusion of Phonotaxis by Masking Sounds in the Bushcricket Conocephalus brevipennis (Tettigoniidae: Conocephalinae)

Female Conocephalus brevipennis, executing phonotaxis to the call of a conspecific male broadcast from a speaker, were subjected to varying levels of background sound so as to progressively mask the attracting signal. The background consisted of either random noise or the call of a sympatric congener, C. nigropleurum and was delivered from above the orienting female. Disruption of phonotaxis was assayed by monitoring the angular dispersion of the female's exit path from the arena, relative to the position of the conspecific call. Random noise significantly interfered with phonotaxis when it was within 2 dB of the conspecific call intensity, both signals measured at the centre of the arena. The equivalent effect of the call C. nigropleurum was 5 dB above conspecific call intensity. The implication of signal loss within background noise is discussed as are the possible interactive behaviours of competing sympatric syntopic species.