The Potential of Biocontrol Agents for the Control ofDiuraphis noxia(Homoptera: Aphididae) in Spring Barley in the Central Highlands of Ethiopia

Investigations were carried out in spring barley, Hordeum vulgare L., fields to determine the abundance of the Russian wheat aphid, Diuraphis noxia (Kurdj.), and associated natural enemies and to evaluate the potential of these natural enemies as biocontrol agents. There was a significant difference in the density of D. noxia among the various sampling dates, the average for the season being 16.7 aphids tiller−1. Surveys and field countings carried out over several seasons and localities indicated that the pest is highly abundant in the region. Among predators recorded, coccinellids and syrphids were found to be more abundant; however, the coccinellid beetle, Hippodamia variegata Goeze, was the dominant species of all predators. Moreover, syrphid fly larvae were the only predators consistently found feeding on aphids within D. noxia rolled up leaves. The quantitative analyses based on predator units (PU) also showed a highly significant difference among the predator groups, the average for the whole predator community being 17.4 PU m−2. Among the parasitoids recorded, Aphidius colemani Vier, was the most abundant species; however, their diversity was very low. The rate of parasitism was also generally low, < 13%. 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.