Field parasitism and host specificity of Oobius primorskyensis (Hymenoptera: Encyrtidae), an egg parasitoid of the emerald ash borer (Coleoptera: Buprestidae) in the Russian Far East

Oobius primorskyensis Yao and Duan (Hymenoptera: Encyrtidae) is a recently described egg parasitoid of the emerald ash borer (EAB), Agrilus planipennis Fairmaire, from the Russian Far East. To support the potential introduction of this new parasitoid for biocontrol of EAB in North America, we surveyed EAB eggs on infested green ash (Fraxinus pennsylvanica Marsh) trees in the Russian Far East and documented the rate of EAB egg parasitism by O. primorskyensis. After establishing quarantine colonies of O. primorskyensis in the United States, we tested the parasitoid against eggs of 30 taxa of insects, mostly native North American wood-boring beetles in the families Buprestidae and Cerambycidae plus one unidentified weevil, one predatory coccinellid, one pentatomid and one moth. Field observations showed that EAB egg parasitism rate ranged from 23 to 44% in the Russian Far East and O. primorskyensis was the only egg parasitoid recovered from the parasitized eggs collected there. Quarantine testing showed that O. primorskyensis attacked seven out of nine Agrilus species, but not any of the other non-target species tested. Percentage parasitism of A. anxius (40%) and A. cephalicus (30%) was comparable to parasitism of their corresponding EAB (positive) control (29-30%). However, percentage parasitism of the other five attacked species (A. bilineatus, A. egenus, A. fallax, A. macer, and A. oblongus) were significantly less (4-17%) than for the EAB control (60-90%). These results indicate that the host specificity of O. primorskyensis may be limited to species phylogenetically closely related to EAB, such as those in the genus Agrilus. Additional testing is needed to determine whether the eggs of other buprestid genera are utilized by the species as well.