The dorsal organ in female antennae of Neodrynus typhlocybae (Ashmead) (Hymenoptera: Drynidae): an auditory function?

Neodryinus typhlocybae (Ashmead) (Hymenoptera: Dryinidae) is a natural enemy of the planthopper Metcalfa pruinosa (Say) (Hemiptera: Flatidae), introduced from North America into Europe and regionally established as a pest species. Vibrational signals play a crucial role in communication of M. pruinosa and probably this characteristic is exploited by the N. typhlocybae. SEM and TEM observations showed in N. typhlocybae female antennae peculiar and complex sensory structures appearing as longitudinal and deep grooves, housing a long sensillum trichoideum. This sensillum extend for all the length of the grooves, without any contact with the grooves cuticle. Its hair shaft is empty and aporous inserted in a specialized socket, underneath which a cuticular ampulla-like chamber is present. Two sensory neurons are present of which one outer dendritic segment terminates at the dendritic sheath proximal end while the other continues into the sensillar sinus enclosed in the dendritic sheath, and then enters the ampulla-like chamber through the circular opening terminating with a conspicuous tubular body at the shaft base. Antenna stimulations, recording of action potentials and signal analysis, prove that the discharge of action potentials from the N. typhlocybae antenna was indeed elicited by vibrational stimulation.