Phonotactic behaviour of a parasitoid fly (Emblemasoma auditrix, Diptera, Sarcophagidae) in response to the calling song of its host Cicada (Okanagana rimosa, Homoptera, Cicadidae)

Males of the cicada Okanagana rimosa emit acoustic signals that attract sex ually receptive conspecific females. This acoustic signal is also used by f emales of the parasitoid fly Emblemasoma auditrix to home in on the cicada and infest it with larvae. In a field study we investigated factors influen cing the phonotactic behaviour of the fly by attracting them to broadcasted natural and artificial acoustic signals. The success of attraction depende d on weather conditions and was best in sunny conditions with temperatures above 25 degreesC. Attraction of flies correlates with that of female cicad as, indicating that both have the same preferences. By varying parameters f ound in the natural calling song, we showed that frequencies and rhythm pat terns which closely resemble the host signal were most attractive. Female c icadas also responded to the signals sooner and arrived earlier at the loud speaker (median latency 16 seconds) than the first fly (median latency 35 s econds), perhaps an adaptive behaviour to the parasitism. The behavioural a uditory threshold intensity of E. auditrix was around 70dB SPL.