Auditory behaviour of a parasitoid fly ( Emblemasoma auditrix , Sarcophagidae, Diptera)

Abstract

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.

Auditory Sensitivity of an Acoustic Parasitoid (<i>Emblemasoma</i> sp., Sarcophagidae, Diptera) and the Calling Behavior of Potential Hosts

“…Thus, the tuned physiological response shown here suggests that there is either intrinsic (e.g., physiological) tuning or subsequent mechanical mechanisms that filter stimuli around the T. pruinosa spectrum [see Lakes-Harlan et al, 1999]. Considering our results, the mismatch in tuning found in E. auditrix is not a characteristic of this taxon and, at least with respect to the O. rimosa song, phonotactic decisions by E. auditrix are made with less than optimal frequency information [Hennig et al, 2004]; such an interpretation is consistent with the broad tuning of the E. auditrix behavioral response [Köhler and Lakes-Harlan, 2001]. …”

“…Thus, the response proportion at 10 m separation, Δ6 dB is important because it serves as a control for use of the threshold to set the normalized separation to 1.0. The response proportion for this condition (0.241 to quieter source; table 2) is nearly identical to that predicted by the model (0.25 to quieter source; χ 2 =0.011, P = 0.915), suggesting that, like E. auditrix [Köhler and Lakes-Harlan, 2001), ∼69 dB SPL is indeed the response threshold in the field.…”

“…Assuming the model songs are accurate, T. pruinosa appears to be at least one host for Emblemasoma larvae: phonotactic host choice was biased to the T. pruinosa call and attracted only larvapositing females. Similar to the response of E. auditrix to artificial signals [Köhler and Lakes-Harlan, 2001], the success of the model T. pruinosa song also shows that the "wind-up" and "wind-down" sections of the call are not necessary for fly phonotaxis. The large response to the T. pruinosa call not withstanding, these data are not conclusive as to host specificity.…”

“…Second, sensitivity in Emblemasoma auditrix (genus formally Colcondamyia; Pape, 1990] differs from the two patterns in ormiines, as whole nerve recordings from interneurons in the neck connectives show evidence for a tuning mismatch: best responses occur at 5 kHz, nearly an octave below the dominant frequency of its host's song (9 kHz), suggesting discrimination between songs of different cicada species is not based on spectral cues [Köhler and LakesHarlan, 2001]. In addition to the tuning mismatch, E. auditrix also exhibits a sharp decrease in physiological sensitivity to low frequencies (<5kHz) [Lakes-Harlan et al, 1999;Köhler and Lakes-Harlan, 2001]. Having data on the sensitivity of only one sarcophagid species, of course, leaves the question open as to the extent of convergence with ormiines; that is, whether the mechanisms and patterns of sensitivity consistently differ between the analogous traits.…”

Collection and Laboratory Culture of Ormia ochracea (Diptera: Tachinidae)

“…Typically, a loudspeaker is used to broadcast an audio signal that mimics the sounds of the parasitoids' hosts, and parasitoids that are attracted to the loudspeaker are either collected by hand (e.g., Soper et al 1976;Fowler & Kochalka 1985;Wagner 1996;Lakes-Harlan et al 2000;Köhler & Lakes-Harlan 2001;de Vries & Lakes-Harlan 2005;Wagner & Basolo 2007) or captured using sticky traps (e.g., Fowler 1987;Walker 1993;Allen 1998;Kolluru & Zuk 2001), electrified wire grids (Mangold 1978;Walker 1986), or custom-built live traps (e.g., Cade 1975Cade , 1979Fowler 1988;Walker 1989;Allen et al 1999). However, if non-destructive, automated sampling is desired, then live traps are the only viable option.…”