Abstract
AbstractThe influence of natural enemies on the population growth of Diuraphis noxia (Mordvilko) in wheat fields in eastern South Africa was investigated. Since the natural enemies were not present in the initial stages, the apparent mortality observed must have been due to other causes. During the logarithmic phase of aphid population growth, predators, in particular the coccinellid Hippodamia variegata (Goeze), had a slight inhibitory effect on growth. During the decline phase of the aphid population, the potential population size was reduced by as much as 52% by predation. The most abundant parasitoids, Aphidius colemani Viereck and Diaeretiella rapae (M'Intosh), had a negligible effect. Although natural enemy populations showed functional responses to increases in Diuraphis noxia numbers, they did not prevent the latter from attaining and exceeding economic injury levels.
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