Utility of Facultative Secondary Parasites in Biological Control

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Abstract
The effect of Zatropis capitis Burks, a facultative secondary parasite, on Torymus koebelei (Huber) and Platygaster californica (Ashmead), primary parasites of Rhopalomyia californica Felt, is used to illustrate how a facultative secondary parasite can be of value in biological control. Parasitization by either of the primary parasites was greatest when these species occurred alone compared to when they occurred in combination with Z. capitis ; however, total parasitization was greatest when the primaries occurred with the facultative secondary parasite. It is suggested that a facultative secondary parasite is of value in biological control when (1) the impact on host density produced by a primary parasite and a facultative secondary one acting in concert is greater than that produced by the primary parasite acting alone and (2) the facultative secondary parasite does not have a deleterious effect on other parasite guilds in the environment.