Background: 'Eavesdropping' parasitoids find their hosts by homing in on the communication signals of other insects. These parasitoids often exploit chemical communication, but at least some species of the sarcophagid genusEmblemasomaeavesdropon the acoustic communications of cicadas. Despite considerable scientific interest in acoustic parasitoids, we know remarkably little about most species of Emblemasoma. To better understand the ecology and behavioral diversity of these flies, I used a combination of field and laboratory techniques to elucidate theinfection behavior and life history of E.erro,which uses the cicada Tibicen dorsatusasa host, and I also investigated parasitoid loads and parasitism rates of T.dorsatus inmultiple host populations in the central United States.
Results: Female E. erro used the acoustic signals of male T. dorsatus as the primary means of locating hosts, but they also required physical movement by the host, usually either walking or flight, to provide visual cues for the final larviposition attack. Larvae were deposited directly on the host's integument and burrowed through intersegmental membrane to enter the host's body. On average, E. erro larvae spent 88.0 h residing inside their host before leaving to pupariate, but residence time was strongly dependent on both ambient temperature and effective clutch size. Adult flies eclosed about 18 days after pupariation. Across all study sites, the mean parasitoid load of infected male T. dorsatus was 4.97 larvae/host, and the overall parasitism rate was 26.3%. Parasitism rates and parasitoid loads varied considerably amonghost population samples, and high parasitism rates were usually associated with high parasitoid loads.
Conclusions: Previously, detailed information about the infection behavior, life history, and host parasitism rates of sarcophagid acoustic parasitoids was only available for one species, E. auditrix. This study reveals that the infection behavior of E. erro is quite different from that of E. auditrix and, more broadly, unlike that known for any other species of acoustic parasitoid. The life histories of these two Emblemasoma are also divergent. These differences suggest that sarcophagid acoustic parasitoids are more behaviorally and ecologically diverse than previously recognized and in need of further study.
Keywords: Eavesdropping; Emblemasoma; Host defense; Host location; Infection behavior; Parasitoid; Parasitoid load; Phonotaxis; Superparasitism; Tibicen.
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