Auditory Parasitoid Flies Exploiting Acoustic Communication of Insects

Abstract

Hearing evolved in flies of both Dipteran families Tachinidae and Sarcophagidae, enabling the parasitic exploitation of singing orthoptera and hemiptera. Guided by acoustic communication signals, these flies identify and localise their singing target, depositing their larvae on or near the host. Larvae then develop as endoparasites, eventually killing the host. In these flies, the mechanosensory auditory organ is located on the prosternum and in most cases is less than one millimetre in size. The frontal facing tympana constitute an extreme example of adaptation in auditory micromechanics. Directional hearing relies on the mechanical coupling between the hemilateral tympana, a purely mechanical process that exploits minute interaural time differences in tympanic vibrations and enhances bilateral oscillation differences to generate a highly directional sensitivity. In tachinid fly species, the frequency response of the ears is adapted to the host communication signals. The auditory organs contain up to 250 scolopidial afferents, which are directly driven by tympanic membrane vibrations. The signals from the auditory afferents are forwarded to auditory neuropils in the three thoracic neuromeres. Further processing of intensity and directional information and also of temporal patterns involves local and also ascending auditory interneurons, which project up to the brain for final sensory-motor integration.