Plant surface mediates interaction between true bug chemical footprints and scelionid egg parasitoids

Chemical footprints left behind by true bugs act as contact kairomones inducing an arrestment response in scelionid egg parasitoids. Once in contact with contaminated substrates, female wasps display a characteristic arrestment posture followed by an increase of the host searching time. Previous studies were conducted on artificial substrates as filter papers, so that little is known about the effects of natural substrates on behavioural response by wasps. In field, the substrate where these interactions occur, i.e. the surface of plants, is covered by wax layers that can have a role in trophic interactions between insects. In this study, we investigated the influence of plant surfaces on absorbing chemical footprints of the true bug Nezara viridula (L.) and on influencing the host location behaviour of the scelionid Trissolcus basalis (Wollaston). Nezara viridula males and females were allowed to walk on leaves artificially dewaxed and leaves with intact superficial layers of three different plants, broad bean, sweet pepper and cabbage. Bioassays suggest that leaf waxes absorb chemical footprints of N. viridula, so that the response of T. basalis females was less pronounced on leaves where superficial waxes were removed using an aqueous solution of arabic gum. Furthermore, a chemical investigation was conducted on the polimer film peeled off from leaves contaminated by N. viridula. In conclusion, our findings demonstrated that surface of studied plants mediates interaction between N. viridula chemical footprints and T. basalis.