Female phonotaxis and frequency discrimination in the bushcricket Requena verticalis

ABSTRACT. The male bushcricket, Requena verticalis , calls with a signal containing two predominant frequencies, 16 kHz and 28 kHz. A synthesized call, made from a template of the natural call, was played to females under conditions of a two-speaker trial on a flat arena. Orientation pathways to a speaker emitting only a 16 kHz signal were more circuitous than the pathways made by females orientating to a speaker emitting only a 28 kHz signal. Females preferred a signal with both carrier frequency peaks present within the song to a signal with only a 16 kHz or 28 kHz carrier frequency, when the signal containing a double peak was kept at equivalent absolute intensity to that with a single peak. Females chose signals containing a more powerful high frequency peak over a signal in which both peaks were balanced. For the higher peak, they were able to differentiate between frequencies with a separation of 8 kHz but not of 4 kHz. They were unable to differentiate between frequencies with a separation up to 8 kHz in the lower peak when one frequency was held at 16 kHz; however, when this frequency was held at 18 kHz, females were able to distinguish between frequencies with a difference of 4 kHz. ( N.B. 18 kHz is 2 kHz above the mean value for this frequency within the natural population.) We conclude that females are choosing males on the amount of power in the higher frequency range of their song and that this may be equivalent to a close calling male in the field.