PARASITOID VIBRATIONS AS POTENTIAL RELEASING STIMULUS OF EVASIVE BEHAVIOR IN A LEAFMINER

The aim of this study was to characterize the vibratory signals produc ed by the parasitoid Sympiesis sericeicornis Nees (Hymenoptera: Euloph idae) while foraging on apple leaves infested by one of its hosts, the spotted tentiform leafminer Phyllonorycter malella (Ger.) (Lepidopter a: Gracillariidae). This leafminer changes its behaviour as a function of the parasitoid's behaviour to escape parasitization. We propose th at the leafminer uses vibrations triggered by the parasitoid to detect the presence of its enemy. We measured vibrations produced by a forag ing parasitoid on a mine with a laser vibrometer. By recording concurr ently the behaviour of the parasitoid on video, vibrations could be as signed to particular behaviours. Subsequently, vibrations were charact erized by their dominant frequencies and intensities. The behaviours L anding and Take-off both produced strong impact-like vibrations charac terized by an initial irregular phase during which frequencies up to 2 5 kHz occurred followed by a slow decaying regular phase. Vibrations e licited by Moving, Standing and Probing showed no clear temporal patte rn. During Probing, dominant frequencies of up to 5.6 kHz were observe d frequently at intensities well above the background noise (> 10 dB). During Moving and Standing, vibrations were more scarce and of lower frequencies and intensities. Due to their impact-like nature, vibratio ns produced by Landing and Take-off are probably not specific to the p arasitoid. Vibrations produced by Moving and Standing are difficult to detect and not reliable because of their non-specificity. Therefore, only Probing provides a reliable and detectable source of information for the host, The vibrations elicited during Probing could account for the evasive behaviour that is observed in this and other leafminers.