Parasitoids and biocontrol of Russian wheat aphid, Diuraphis noxia (Kurdj.) expanding in central Europe

Hymenopterous parasitoids found on the Russian wheat aphid (RWA), Diuraphis noxia (Kurdj.) since the aphid was detected in the Czech Republic in 1995 have been studied. Parasitoids were obtained from aphid samples taken in small grains and from field exposures of banker-units containing laboratory mass-reared RWA. The parasitoid species are listed. Their presence on RWA was verified and their host species alternation was also tested in the laboratory. Evidence on some species was obtained only through unnatural host propagation. Aphidius colemani Vier. (a Chilean strain) was purposely introduced, released and became established; its host range, which included both target and nontarget species, is listed. Prediction versus determination of RWA parasitoid complex in central Europe are discussed and the field samples and the exposure trials are compared. The RWA presence in relation to biodiversity in the small-grains agroecosystem is analysed. An overall parasitoid spectrum of RWA in the Old World (and the world background) is reviewed in relation to the RWA native range and the distribution (expansion) range, respectively. A corresponding analysis of the central European situation, derived from the expansion route of RWA to the Mediterranean, is presented.