Rhopalamyia califarnica Felt is an endemic cecidomyiid midge which develops within terminal galls on Baccharis pilularis DC in California. Individual galls normally contain more than one larva and can thus be viewed as discrete host patches in space and time. At the Jasper Ridge Biological Preserve, the number of midge larvae per gall varied from 1 to 40 and individual galls were exploited by as many as five species of parasites. Total percentage of parasitization per gall was relatively constant, regardless of the number of host larvae per gall. Instead of being density-dependent, total mortality was species dependent–the proportion of hosts parasitized per gall was directly related to the number of species of parasites reared from the gall. However, the total proportion of hosts parasitized in the samples was relatively low (37.5%) because most galls contained either zero or one species of parasite. Less than 1% contained five species and less than 5% contained four species. The evidence is consistent with the hypothesis that this guild is structured so as to reduce the incidence of interspecific competition among the parasites, and it raises the possibility that the structure of a parasite guild may not necessarily be compatible with the goals of biological control. I suggested that parasite guilds such as this one might be “restructured” so as to actually increase their efficiency in maintaining pest populations at relatively low levels. Additional aspects of restructuring parasite guilds are discussed.
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L. E. Ehler (1985) studied this question.