Diaeretiella rapae M'Intosh is a cosmopolitan parasitoid of several pest aphid species in agroecosystems, including the Russian what aphid, Diuraphis noxia (Mordvilko) (Mackauer and Stary 1967). In recent years, D. rapae has been imported into the United States from regions throughout the world for D. noxia classical biological control. Knowledge of the alternative hosts of D. rapae could be useful for identifying ecosystems into which the parasitoid could be released at times when D. noxia is absent. Over 30 aphid species are listed as hosts of D. rapae (Mackauer and Stary 1967). This host list, though comprehensive, is a compilation of information gathered from diverse, mostly unrelated sources, and does not necessarily depict the host range of any particular population. Host range differs among populations of some aphidiid species collected from different regions or from different hosts in the same region (Powell 1986). Thus, published host lists can be misleading if they are the sole source of information used to determine acceptable alternative hosts on which to release prospective candidates in classical biocontrol programs. The purpose of this study was to determine the relative suitability of several aphid species common to agricultural and associated non-agricultural ecosystems in the Great Plains as hosts for this Syrian D. rapae isolate in laboratory no-choice tests.