Role of volatile semiochemicals in host location by the egg parasitoid Anagrus breviphragma

Recent investigations conducted on several tritrophic systems have demonstrated that egg parasitoids, when searching for host eggs, may exploit plant synomones that have been induced as a consequence of host oviposition. In this article we show that, in a system characterized by host eggs embedded in the plant tissue, naı¨ve females of the egg parasitoid Anagrus breviphragma Soyka (Hymenoptera: Mymaridae) responded in a Y-tube olfactometer to volatiles from leaves of Carex riparia Curtis (Cyperaceae) containing eggs of one of its hosts, Cicadella viridis (L.) (Hemiptera: Cicadellidae). The wasp did not respond to host eggs or to clean leaves from non-infested plants compared with clean air, whereas it showed a strong preference for the olfactometer armcontaining volatiles of leaves with embedded host eggs, compared with the arm containing volatiles of leaves from a non-infested plant or host eggs extracted from the plant.When the eggs were removed from an infested leaf, the parasitoid preference was observed only if eggs were added aside, suggesting a synergistic effect of a local plant synomone and an egg kairomone. The parasitoid also responded to clean leaves from an egginfested plant when compared with leaves from a non-infested plant, indicating a systemic effect of volatile induction.