Song power, spectral distribution and female phonotaxis in the bushcricket Requena verticalis (Tettigoniidae: Orthoptera): active female choice or passive attraction

The role of sound as a cue for female choice in the bushcricket Requena verticalis was investigated in both the field and laboratory. Females oriented to the closer of two calling males in a two-male field trial. Preference appeared to depend on the power of the higher frequency components (circa 28 kHz) of the call's spectrum, as well as the variance in chirp rate. Recording the songs of small and large males, and testing females on a two-speaker laboratory arena, revealed that when absolute call intensities were held at the same level, females could not distinguish between males from different size classes. However, where a consistent speaker preference occurred to a recording of either a large or small male, preference was shown towards the speaker producing a song with the greater power in the high frequency part of the spectrum. When the call of a single male was duplicated and presented as a choice to the female at different intensities, females were able to differentiate the call with an intensity difference of 1 dB in calls where the low frequency was more pronounced than higher frequencies, and with a 3 dB difference where this balance was less pronounced. Acuity, as expressed by the distance the female travelled before reaching the speaker, was improved where higher frequencies were more pronounced.