Recovery and range expansion of parasitoids (Hymenoptera : Aphelinidae andBraconidae) released for biological control of Diuraphis noxia (Homoptera : Aphididae) in Wyoming

Aphelinus albipodus Hayat & Fatima, A. asychis Walker (Hymenoptera: Aphelin idae), Diaeretiella rapae (M'Intosh), Aphidius matricariae Haliday, Aphidiu s colemani (Viereck), Aphidius picipes (Nees), Aphidius rhopalosiphi DeStef ani-Perez, Ephedrus plagiator (Ness), and Praon gallicum Stary (Hymenoptera : Braconidae) were released in southeastern Wyoming for biological control of Diuraphis noxia (Mordvilko), Russian wheat aphid (Homoptera: Aphididae). A total of 407,028 parasitoids in the form of mummified aphids was release d from 1989 to 1996. Three species, A. albipodus, A. asychis, and D. rapae, were first detected in winter wheat fields 3 yr after first release and sp read throughout the wheat production region within 5 yr of release. Other p rimary aphid parasitoids were recovered sporadically and in very small quan tities, and hyperparasitoids consisted of up to 20% of the specimens recove red. There were significant differences in abundance of A. albipodus, A. as ychis, and D. rapae. In 1992, D. rapae was more abundant than the two aphel inids. By 1995, A. albipodus was becoming more prevalent than D. rapae, and A. albipodus was the most abundant species in 1997 and 1998. During these 2 yr, A. albipodus and D. rapae were detected in small grain fields and adj acent grasslands in similar abundance in both habitats. Of the parasitoids released in the D. noxia biological control program, A. albipodus and D. ra pae commonly occurred in wheat and barley of southeastern Wyoming, with occ urrence of the exotic A. albipodus directly attributable to the release eff ort. A. albipodus is likely becoming the predominant species in small grain production in the region. And A. albipodus and D. rapae range expansion an d occurrence in grassland sites adjacent to wheat and barley may aid in the ir ability to control D. noxa.