Abstract
During the host location process, egg parasitoids can eavesdrop on chemical cues released from immature and adult hosts. These indirect host-related cues are highly detectable, but of low reliability because they lead egg parasitoid females to an area where oviposition is likely to occur rather then providing wasps with direct information on the presence of eggs and their location. In the host-parasitoid associations between true bugs and their scelionid egg parasitoids, female wasps perceive the chemical residues left by host adults walking on substrates as contact kairomones, displaying a characteristic arrestment posture. In this study, we demonstrated that epicuticular waxes of leaves of two vegetable crops, broad bean, Vicia faba and collard greens, Brassica oleracea, mediate the foraging behaviour of Trissolcus basalis (Wollaston) by adsorbing contact kairomones from adults of Nezara viridula (L.). Trissolcus basalis females showed no response when released on the adaxial leaf surface of broad bean or collard green plants with intact cuticular wax layers that had not been exposed to bugs, whereas wasps displayed the arrestment posture when intact leaves were contaminated by chemical residues from host females. Adaxial leaf surfaces that were dewaxed with an aqueous solution of gum arabic and afterwards contaminated by N. viridula females elicited no arrestment responses from wasp females. Similarly, leaves contaminated by host females and subsequently dewaxed did not elicit responses from female wasps. These findings reveal the important role of plant waxes in N. viridula-T. basalis semiochemical communication.