Evaluation of the host specificity of Spathius galinae (Hymenoptera: Braconidae), a larval parasitoid of the emerald ash borer (Coleoptera: Buprestidae) in Northeast Asia

• Spathius galinae is a new parasitoid of the emerald ash borer (EAB), Agrilus planipennis, in the Russian Far East (RFE).
• Field survey in the RFE revealed no attacks on other ash borers other than EAB.
• It attacked only one nontarget species of 15 tested North American wood bores – i.e., the congener Agrilus auroguttatus.
• Parasitism rate of A. auroguttatus is significantly lower than that of A. planipennis.
• Host specificity of S. galinae may be phylogenetically limited to the genus Agrilus.

Host-specificity determination prior to the introduction of non-native natural enemies is a critical component of the risk assessment for modern classical biocontrol programs. In the present study, we assessed the host specificity of a newly described parasitoid, Spathius galinae Belokobylskij and Strazanac, which is native to Northeast Asia, for classical biocontrol of the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire, in North America. Along with foreign exploration for natural enemies of EAB in 2010 and 2012, we surveyed ash (Fraxinus spp.) wood-boring insects and their parasitoids from artificially stressed Oriental ash (F. rhynchophylla Hance) trees in natural forest stands in the Primorskiy Kray region of Russia. Once colonies of S. galinae were established in U.S. quarantine, we tested the parasitoid against 15 species or groups of North American wood-boring insects that were selected along a continuum from closely related taxa (e.g., Agrilus spp. in the family Buprestidae in Coleoptera) to distantly related ones in Lepidoptera and Hymenoptera. While three of the tested insects, Neoclytus acuminatus Fabricius, Podosesia spp. and Hylesinus fraxini Panzer attack ash as their main host, the rest attack non-ash trees such as birch, maple and oak. Results from our field survey in Russia showed that S. galinae did not attack bark beetles (Hylesinus spp.) or longhorned beetles (Cerambycidae) that coexisted with EAB on infested ash trees. In quarantine laboratory studies, S. galinae did not attack 14 species or groups of non-target wood-boring insects infesting both ash and/or non-ash trees such as birch, maple or red oak. The only non-target attack was on the goldspotted oak borer (GSOB), Agrilus auroguttatus Schaeffer, infesting red oak. The rate of parasitism on GSOB was significantly lower than on EAB under laboratory conditions that favored parasitism. These findings indicate that the host specificity of S. galinae is restricted within the host genus (Agrilus).

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