Species diversity, abundance, and phenology of aphid natural enemies on spring wheats resistant and susceptible to Russian wheat aphid

The species composition, relative abundance, and seasonal dynamics of selected natural enemies of cereal aphids were monitored in spring wheat fields in Moscow, Idaho in 1997 and 1998. Trials also examined the potential impact of resistance to Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) (Homoptera: Aphididae) in wheat, on aphid biological control agents. Natural enemy populations were monitored on two spring wheats: D. noxia susceptible variety 'Centennial' and resistant genotype 'IDO488'. Field plots were artificially infested with adult D. noxia, and sampled for cereal aphids and parasitoids weekly. Coccinellid predators were monitored once in 1997 and twice in 1998. The coccinellids Hippodamia convergens Guerin, Coccinella septempunctata L., C. transversoguttata Brown and C. trifasciata Mulsant were detected. No significant differences in adult or immature coccinellid densities were observed between the D. noxia resistant and susceptible genotypes. During both years, the most abundant primary hymenopteran parasitoids were Diaeretiella rapae (M'Intosh), Aphidius ervi Haliday, A. avenaphis (Fitch), and Lysiphlebus testaceipes (Cresson), Aphelinus varipes (Foerster), Aphidius colemani Viereck, Aphidius picipes (Nees), Aphidius sp., Monoctonus washingtonensis Pike & Stary, Praon gallicum Stary, Praon occidentale Baker, and Praon sp. were also detected. Numbers of both D. noxia and D. rapae were significantly greater on Centennial than on IDO488 in both years. When all species of cereal aphids and parasitoids are considered, the total percentage parasitism was not significantly different between the genotypes. There was no interaction between D. noxia resistance and the population density of the predators or parasitoids monitored. These results suggest that the D. noxia resistant line had no adverse impact on natural enemies under the conditions of these field experiments.