Bionomics of Encarsia scapeata Rivnay (Hymenoptera: Aphelinidae), tritrophic relationships and host-induced diapause

During a survey of whitefly parasitoids in the Israeli Mediterranean forest, we found Encarsia scapeata Rivnay to be the only parasitoid of Trialeurodes lauri Signoret, growing on Arbutus andrachne L. trees. Overall parasitism levels averaged about 10% during the two-year study and correlated inversely with whitefly abundance. Following bud burst, the univoltine whiteflies oviposit on the young leaves (April–May), develop to the early 4th instar and then diapause from May–June to next spring, when their development to mature adults continues. Following a diapause that had apparently been induced by the whitefly host, most adult parasitoids emerged during April, intimately synchronized with their whitefly host. Natural diapause of the whiteflies and the wasps could be experimentally broken by cutting infested branches and keeping them under room conditions. Analyses of slide-mounted material revealed that parasitoid development usually occurred following initiation of post-diapause development in the unparasitized whiteflies of the same age, but occasionally preceded it. This host-dependent phenological plasticity of E. scapeata ensures synchronization with its hosts in the heterogeneous forest environment. In a lab set-up, E. scapeata readily parasitized the non-diapausing whitefly Bemisia tabaci (Gennadius), in which it too did not diapause. Thus, the diapause of E. scapeata is apparently induced by the diapause of its whitefly host. Since it can successfully develop on B. tabaci, E. scapeata, with its flexible developmental strategy, could serve as an addition to the pool of Encarsia species useful for B. tabaci control.