Predation experiments were conducted in the laboratory to study the potential effect of Orius tristicolor (White) on the widely used spider mite predator, Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae). In a 24-h test on English cucumber leaf disks surrounded by a water barrier, we measured rates of escape and mortality of P. persimilis when exposed to O. tristicolor alone or in the presence of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and two-spotted spider mites, Tetranychus urticae Koch (Acarina: Tetranychidae), which acted as alternate prey. O. tristicolor killed P. persimilis in significant numbers even when thrips were available. The addition of spider mites and thrips to the two predator system significantly reduced O. tristicolor predation on P. persimilis and thrips. Spider mites were shown to reduce O. tristicolor predation both through adult mites substituting as acceptable prey and through the mite's webbing acting to lower overall preying activity of O. tristicolor . When spider mites were available, a negative correlation was observed between thrips killed and P. persimilis surviving, indicating no clear preference of O. tristicolor for attacking thrips rather than P. persimilis . We discuss the significance of the generalized character of O. tristicolor attack behavior with respect to its use as a thrips predator in the greenhouse, and the potential significance of our laboratory observations for situations requiring biological control of multiple pests.
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Cloutier et al. (1993) studied this question.
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