Recovery of imported hymenopterous parasitoids released to control Russianwheat aphids (Homoptera : Aphididae) in Colorado

From 1991 through 1993 exotic parasitoids of the Russian wheat aphid, Diura phis noxia (Mordvilko), were released in eastern Colorado in an attempt to establish natural enemies for biological control in small grain agroecosyst ems. Seven species, Aphelinus albipodus Hayat and Fatima, Aphelinus asychis Walker. Aphelinus varipes (Forester). Aphidius colemani (Viereck), Aphidiu s matricariae Haliday, Diaereriella rapae (M'Intosh), and Ephedrus plagiato r (Nees), from D. noxia's aboriginal home of Eurasia were introduced into a phid-infested wheat fields. Three years later, three aphelinid species A. a lbipodus, A. asychis, and A. varipes, and a putative Chinese strain of D. r apae, have become established over a six state region. A. albipodus, A. var ipes, and D. rapae were also recovered from greenbugs, Schizaphis graminum (Rondani), on sorghum, Sorghum bicolor (L.) Moench. A. albipodus and D. rap ae successfully parasitized D. noxia on several non-cultivated grasses that serve as oversummering hosts. Summaries of parasitoid recoveries and their host and plant species associations are discussed.