We compared the performance of three Metaphycus spp. (Hymenoptera: Encyrtidae) as potential biological control agents of black scale, Saissetia oleae (Olivier), on southern California citrus. Metaphycus sp. nr. flavus (Howard), Metaphycus helvolus (Compere), and Metaphycus luteolus (Timberlake) were released into sleeve cages covering black scale infested citrus branches. As indicators of biological control, we assessed scale survival and the percentage of scales parasitized by Metaphycus spp. Three release timings were evaluated (11 November, 24 December, and 28 February). For each release date, terminals were retrieved on three occasions (0.5–1 mo after release, 1.5–2.5 mo after release, and immediately before female scales began reproducing, i.e., mid-May to mid-June). Only M. sp. nr. flavus significantly reduced black scale survival and increased parasitism rates compared with background levels. Metaphycus helvolus showed a tendency to reduce scale survival, although no effect of M. luteolus was evident. To further evaluate M. sp. nr. flavus, an open-field release experiment was performed. An excess of 2,700 female parasitoids per tree, released over a period from January to April, significantly reduced black scale survival and increased parasitism on the trees where the parasitoids were liberated. A tendency of increased scale parasitism on trees adjacent to release trees was observed, but no effect on scale survival was evident. Given our results, and considering that M. sp. nr. flavus can be reared on brown soft scale, Coccus hesperidum L., which is easier to rear than black scale, the required host for M. helvolus, developing M. sp. nr. flavus as an augmentatively released biological control agent against black scale may result in more economic biological control than is the case with the currently released M. helvolus.
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