Acoustic attraction of the parasitoid fly Ormia ochracea to the song of its host

Abstract

The parasitoid fly O. ochracea locates its cricket host by acoustically detecting its calling song. The phonotactic abilities of the fly’s auditory system were investigated behaviorally. Phonotaxis was investigated in a large (w 2.5×14.5×h 3<th>m), sound-proofed, flight cage equipped with loudspeakers. Simulated cricket calls with different carrier frequencies including the standard song (4.8 kHz, 45 pps, 13-ms pulse length) were played back to attract the flies. Behavioral threshold curves were established by varying the sound pressure level (SPL) for songs with different frequencies (3.5 to 6.0 kHz). Threshold was determined when phonotaxis failed to occur but was validated only if the fly subsequently reacted to the next higher SPL in the intensity series. Between 4.5 and 5.2 kHz, thresholds were observed to be around 40 dB (re: 20 Pa; i.e., at 4.8 kHz: 38.3 dB, s.d.=3.0 dB, n=5 animals). The sensitivity of phonotaxis to the level of masking noise was also tested by masking songs of different frequencies with varying noise levels. Noise-threshold curves show the behavior to be least affected by noise at 4.8 kHz, where successful phonotaxis to a 60-dB SPL song occurs up to a masking noise level of 45.3 dB SPL. However, at the frequency of best physiological threshold (5.0 kHz), masking occurs at 39.0 dB SPL. [Work supported by the Swiss Science Foundation.]