Females of the parasitoid fly Emblemasoma auditrix find their host cicada (Okanagana rimosa) by its acoustic signals. In laboratory experiments, fly phonotaxis had a mean threshold of about 66 dB SPL when tested with the cicada calling song. Flies exhibited a frequency dependent phonotaxis when testing to song models with different carrier frequencies (pulses of 6 ms duration and a repetition rate of 80 pulses s(-1)). However, the phonotactic threshold was rather broadly tuned in the range from 5 kHz to 11 kHz. Phonotaxis was also dependent on the temporal parameters of the song models: repetition rates of 60 pulses s(-1) and 80 pulses s and pulse durations of 5-7 ms resulted in the highest percentages of phonotaxis performing animals coupled with the lowest threshold values. Thus, parasitoid phonotaxis is adapted especially to the temporal parameters of the calling song of the host. Choice experiments revealed a preference of a song model with 9 kHz carrier frequency (peak energy of the host song) compared with 5 kHz carrier frequency (electrophysiologically determined best hearing frequency). However, this preference changed with the relative sound pressure level of both signals. When presented simultaneously, E. auditrix preferred 5-kHz signals, if they were 5 dB SPL louder than the 9-kHz signal.

Abstract.  1. Females of the parasitoid fly Emblemasoma auditrix find their host cicadas (Okanagana rimosa) using the acoustic signals produced by the host. The phonotactic behaviour of the parasitoid was studied with regard to differently structured habitats. 2. Habitats were modified experimentally within a distance of 2.5 m (approximately the natural range of phonotaxis) from a loudspeaker broadcasting a model of the host calling song. 3. Video analysis showed that in an open habitat (no landmarks) more than 60% of the flies performed a direct flight towards the loudspeaker. 4. In structured habitats (with one to three landmarks) more than 90% of the flies landed on their way to the acoustic target. 5. In about 50% of the landings flies paused for several seconds indicating re‐orientation during that time. Several flies included sequences of walking in their approach behaviour, whereby most walking occurred close to the loudspeaker. 6. In summary, the phonotactic approach and host finding depends on the habitat structure.