PHONOTAXIS IN THE CICADAS CYSTOSOMA SAUNDERSII AND CYCLOCHILA AUSTRALASIAE

Abstract

ABSTRACT 1. Phonotaxis was investigated in two cicada species: Cystosoma saundersii and Cyclochila australasiae. Females were placed on a stick within a flight cage and presented with artificially generated calling songs. These model calling songs had a range of carrier frequencies, but their temporal parameters were similar to those of the natural calling song. They were broadcast at intensities 30 to 40 dB above the physiological threshold for each frequency. 2. Phonotaxis of female Cystosoma saundersii was restricted to a 45 minute period just after sunset, and was highly directional. Between 60 and 70% of flights made during trials in which a model calling song was broadcast were directed towards the loudspeaker at both frequencies tested. 3. Phonotaxis of female Cyclochila australasiae occurred throughout the evening, and showed no directional preference toward the loudspeaker. The mean number of flights per trial period was significantly greater in trials during which a model calling song was broadcast than in control trials during which no model calling song was broadcast. There was no significant difference in the mean number of flights per trial with different carrier frequencies. 4. In female cicadas, acoustic signals of the males are preferentially graded by the tuned auditory system; phonotactic decisions are then made on the basis of relative intensity without active discrimination between frequencies.