SUMMARY The egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) responded to synomones emitted by leguminous plants induced by feeding and oviposition activity of the bug Nezara viridula (L.) (Heteroptera: Pentatomidae). This was shown by laboratory bioassays using a Y-tube olfactometer. Broad bean leaves (Vicia faba L.) damaged by feeding activity of N. viridula and on which host egg mass had been laid produced synomones that attracted T. basalis. By contrast, undamaged leaves or feeding-damaged leaves without eggs did not attract wasp females. French bean plants (Phaseolus vulgaris L.) also emitted attractive synomones when they were damaged by host feeding and carrying egg masses. Thus, release of feeding- and oviposition-induced synomones does not seem to be plant-specific. Synomone production was shown to be a systemically induced plant physiological response to feeding damage and oviposition. Also, parts of the plant that were left undamaged and did not carry host eggs emitted attractive synomones when other parts of the plant were damaged by feeding and carrying eggs. Furthermore, wasps were not attracted by N. viridula egg masses offered alone or combined with damaged broad bean leaves. Thus, the attractiveness of feeding-damaged leaves carrying eggs is due to induction by feeding and oviposition rather than due to a combined effect of attractive volatiles released from eggs and damaged leaves. The production of synomones was influenced by the age of the host egg mass, because feeding-damaged leaves bearing egg masses attracted the parasitoid until the eggs were ∼72-96 h old but not once the larvae had hatched from the eggs (∼120 h old). These results show that annual plants are able to produce synomones as a consequence of feeding and egg mass oviposition by a sucking insect.

Chemical residues left by walking adults of the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae) induce arrestment behavior in the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) leading to prolonged periods of walking on contaminated areas and to systematic return to the stimulus after encountering the treatment borders. In this study, we quantified how the hierarchical value of residues from host adults and oviposition experience can influence the arrestment behavior of T. basalis females. Our results showed that: (1) female wasps perceived host residues at different hierarchical levels depending on the host gender, with a clear preference for the chemical residues deposited by host females rather then host males; (2) wasps' arrestment response to chemical residues of host females became weaker when wasps were not rewarded by an oviposition experience, and stronger following successful oviposition; (3) repeated encounters with host male chemical residues, followed or not by oviposition experience, did not cause wasps to change their innate arrestment response; (4) in the unrewarded condition, arrestment responses of wasps varied according to the time elapsed between successive visits to areas contaminated by host females: responses were weak with a short interval (less than 24 h) and stronger with a long interval (more than 72 h), suggesting that this unrewarded experience, i.e. encounter with female traces not followed by host egg location, fade within a few hours. The potential significance of these results to the host location behavior of T. basalis in the field is discussed.