Free-flight phonotaxis in a parasitoid fly: behavioural thresholds, relative attraction and susceptibility to noise.

The phonotactic capacity of tachinid flies to acoustically detect and localize a sound source simulating their cricket host was investigated in a large flight room. Acoustic measurements were performed to estimate the actual stimulus delivered to the flies, revealing highly heterogeneous sound fields. When presented with a simulated cricket song in red or infrared light conditions, the flies readily flew to the sound source and landed on it. Behavioural phonotactic thresholds were established as a function of carrier frequency and were found to coincide well with the frequency of the host's natural song (4.5-5.2 kHz). Experiments revealed that the same range of frequencies is preferentially attractive to the free-flying flies, and that the reliability of signal detection in the presence of noise is best at behaviourally relevant frequencies.