Small-Grain Aphid Parasitoids (Hymenoptera: Aphelinidae and Aphidiidae) of Washington: Distribution, Relative Abundance, Seasonal Occurrence, and Key to Known North American Species

New information is provided on the small-grain aphid parasitoids of eastern Washington—species population diversity, relative abundance, hosts, and spatial and temporal distribution across differing precipitation and cropping zones. In total 13 species of primary parasitoids were discovered attacking grain aphids: Aphelinus albipodus Hayat & Fatima, A. asychis Walker, A. varipes (Foerster), Aphidius avenaphis (Fitch), A. ervi Haliday, A. matricariae Haliday, Diaeretiella rapae (M'Intosh), Ephedrus sp., Lysiphlebus testaceipes (Cresson), Monoctonus washingtonensis Pike & Star´y, Praon unicum Smith, P. occidentale Baker, and P. yakimanum Pike & Starý. The predominant parasitoids were D. rapae on Russian wheat aphid, Diuraphis noxia (Kurdjumov); L. testaceipes on bird cherry-oat aphid, Rhopalosiphum padi (L.) and corn leaf aphid, R. maidis (Fitch); and A. avenaphis, A. ervi , and D. rapae on English grain aphid, Sitobion avenae (F.). This study provides baseline information essential for assessing future changes in aphid parasitoid species dynamics for eastern Washington. A comprehensive key to the known primary and secondary parasitoids associated with grain aphids in North America also is provided.