none The pupal parasitoid Pimpla turionellae uses self-produced vibrations to locate concealed hosts. This so-called vibrational sounding involves the production, transmission as well as detection of vibrations. This study addresses the mechanisms through which P. turionellae detects the resonance of self-produced vibrations. Transmission electron microscope studies provided the first evidence for the existence of a subgenual organ in hymenopteran parasitoids. This receptor organ was found in the tibia of all six legs. A series of bioassays using paper cylinders containing a filter as a model for a concealed host corroborated the role of tarsal contact in vibrational sounding. When the parasitoid's contact with the cylinder is restricted to the antennae, parasitoids are strongly impaired in their ability to locate the host dummy, in comparison to individuals that are allowed both tarsal and antennal contact. The positioning of the tarsi at the time of initiation of probing and turning behaviour indicates that the female compares the vibrations detected via fore-, middle- and hind-tarsi, and uses this information to determine her position with regard to the solid section in the substrate. These behavioural experiments support our hypothesis that the subgenual organ is involved as a mechanoreceptor during the process of vibrational sounding. General morphology; Appendages; Sensory reception Pimpla turionellae (Ichneumonidae); Thoracic legs; Subgenual organ; Ultrastructure & resonance detection of self produced host seeking vibrations; Mechanoreception; Resonance detection of self produced host seeking vibrations