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Augmentative Release Trials with Metaphycus spp. (Hymenoptera: Encyrtidae) Against Citricola Scale (Homoptera: Coccidae) in California’s San Joaquin Valley

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In recent years, citricola scale, Coccus pseudomagnoliarum (Kuwana) (Homoptera: Coccidae), has re-emerged as an important pest of citrus in California’s San Joaquin Valley. We seek a biological control solution to citricola scale’s pest status as part of an evolving, ecologically based integrated pest management (IPM) program for citrus. We report on augmentative release trials against citricola scale involving 4 species of Metaphycus (Hymenoptera: Encyrtidae)—M. flavus (Howard), M. helvolus (Compere), M. luteolus (Timberlake), and M. stanleyi Compere. We released these parasitoids against sleeve-caged citricola scales in a San Joaquin Valley citrus grove. Releases were made on 3 dates (hereinafter “early,” “intermediate,” and “late” release dates), each date representing scales of different size, all between 1 and 1.5 mm in length. Two to 4 of the parasitoid species were released on any of the dates. Relative to a control (no parasitoid release), the M. flavus treatments (2 densities were released) provided the greatest degree of reduction in scale numbers in the early release (from >3,600 to <5 per cage), while M. helvolus had an intermediate effect. In the intermediate release, M. flavus again provided the greatest reduction in scale numbers (from >2,000 to <6 per cage), followed by M. luteolus, whereas M. stanleyi did not differ from the control. In the late release, all parasitoid treatments (M. flavus, M. helvolus, M. luteolus, and M. stanleyi) provided similar degrees of reduction in scale numbers (from ≈1,150 to ≈6 per cage) relative to the control. We discuss the relevance of citricola scale’s size at the time of parasitoid release to the results obtained with each of the parasitoid treatments on each of the release dates. In addition, we discuss the perceived impact of hyperparasitism by a facultative autoparasitoid, Coccophagus lycimnia (Walker), on our results. We conclude that citricola scale’s size at the time of release is particularly important for deciding which parasitoid(s) to release, and that M. flavus and M. luteolus are the most promising parasitoids, among those currently available to us, for further research toward developing augmentative biological control tactics against citricola scale.

Keywords: Coccus pseudomagnoliarum; Metaphycus flavus; Metaphycus helvolus; Metaphycus luteolus; Metaphycus stanleyi; augmentative biological control

Document Type: Research Article

Publication date: October 1, 1999

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  • Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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