Population Ecology of Aphis nerii1 on Oleander

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Abstract
Population ecology of Aphis nerii B.d.F.on oleander ( Nerium oleander L.) in northern California was assessed. A native generalist, Lysiphlebus testaceipes Cresson, was the only primary parasite reared from A. nerii , and in certain cases, it was able to control the host population. However, parasitization by L. testaceipes was an inverse-density-dependent factor and thus not a significant mortality factor at high aphid population densities. The latter populations were apparently regulated through intraspecific mechanisms (e.g., competition). Outbreaks of A. nerii occurred only at urban sites where plants were regularly pruned and watered. These cultural practices resulted in an increased proportion of new, actively growing terminals (preferred by A. nerii ) which led to increased density of aphids feeding on such terminals. Relevance of these studies to insect ecology in urban environments is discussed.