Effectiveness of predators and parasitoids for the natural control of Diuraphis noxia (Homoptera: Aphididae) on barley in central Ethiopia.
The Russian wheat aphid, Diuraphis noxia (Kurdj.), is a serious threat for the production of barley, Hordeum vulgare L., in Ethiopia. The pest can cause up to 100% yield losses in years of heavy infestation. Natural control of D. noxia by using predators and parasitoids might be the best alternative both from economical and ecological point of view. In this regard, a field investigation was conducted during the 2001 spring cropping season at Fitche, central Ethiopia to determine abundance of D. noxia and associated natural enemies and evaluate their effectiveness as natural control agents for this pest. In addition, the data collected during the 1995-1997 spring and summer cropping seasons at Chacha was analysed and presented. There was a highly significant difference (P < 0.01) on the population density of D. noxia between spring and summer and among sampling dates. The average aphid density was 23.1 and 0.7 aphids per tiller during spring and summer, respectively. The quantitative analyses based on predator units (PU) showed a highly significant difference (P < 0.01) among the predator groups, coccinellids and syrphids being more important, however, the coccinellid beetle, Hippodamia variegata Goeze, was the dominant species from all predator species or groups. Moreover, syrphid fly larvae were the only predators consistently found feeding on aphids within D. noxia rolled leaves. The polyphagous predators: Chrysopids, spiders and staphylinids were found to have less effect on D. noxia populations. Only two primary parasitoid species were recorded both during spring and summer cropping seasons: Aphidius colemani Vier. and Aphidius spp. Of these, A. colemani was more abundant in both seasons. The rate of parasitism was also generally low during the season. In general, the population build up of these natural enemies is slow and maximum population size is reached after the aphid population peaks and the crop has already been damaged. Further extensive work is necessary to maximize the effectiveness of natural enemies against this pest.
Adisu
B
B
Federal Biological Research centre for Agriculture and Forestry (BBA), Institute for Integrated Plant Protection, Stahnsdorfer Damm 81, D-14532 Kleinmachnow, Germany.
Freier
B
B
Büttner
C
C
D000818:Animals; D001042:Aphids / Q000472:pathogenicity*; D005002:Ethiopia; D006430:Hemiptera; D001467:Hordeum / Q000254:growth & development / Q000469:parasitology*; D010572:Pest Control, Biological / Q000379:methods*; D011156:Population Density; D011235:Predatory Behavior; D015203:Reproducibility of Results; D012621:Seasons; D014908:Triticum / Q000254:growth & development / Q000469:parasitology*