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The 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.

The rate of development, fecundity and lifespan of apterae of Diuraphis noxia (Mordvilko) were determined at five sets of temperature and daylength conditions. The time required to complete pre-imaginal growth at mean daily temperatures of 10, 13, 14, 17-25 and 20°C was 19-70, 12-09, 11-25, 9-88 and 8-17 days, respectively. The threshold for development was estimated to be 0-54°C and the number of day-degrees C required to complete development was 158-73.

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