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Project description

Augmentative Biological Control of Soft Scale Pests of Citrus. (97BC001)
Program UC IPM competitive research grants program
R.F. Luck, Entomology, UC Riverside
J.G. Morse, Entomology, UC Riverside
K.M. Daane, Biological Control, UC Berkeley/Kearney Agricultural Center
Host/habitat Citrus; Tree Crops
Pest Soft Scales
Discipline Entomology
Biological Controls
Start year (duration)  1997 (Two Years)
Objectives In laboratory experiments, evaluate black scale and brown soft scale as rearing hosts for five of the seven species of parasitoids we have in culture.

Conduct seven series of preliminary field-cage experiments with promising parasitoids (black scale on olives and citrus; citricola scale on citrus; and black, brown soft, green shield, and tulip tree scales on ornamentals), and develop quality control criteria for insectary production of the most promising parasitoid species.

We evaluated parasitoids for biological control of soft scales on California citrus. Four Metaphycus species (M. helvolus, M. stanleyi, M. luteolus, and M. sp. nr. flavus) were tested on citricola scale on San Joaquin Valley, and three species (M. helvolus, M. luteolus, and M. sp. nr. flavus) were tested on black scale in southern California. Known numbers of the parasitoids were released into sleeve cages with scale infested terminals. On citricola scales, we conducted three experiments with releases, on November 1, 1996, December 31, 1996, and February 2, 1997. Another three trials were conducted on black scale (releases on November 11, 1997, December 24, 1997, and February 28, 1998).

The results from these sleeve cage experiments suggest that M. sp. nr. flavus is the most promising candidate against citricola scales. On black scale in southern California, M. sp. nr. flavus performed best in the November and February releases. In the December releases M. helvolus resulted in the lowest number of surviving scales.

Subsequently, from February through May 1998, we performed an open field release trial with M. sp. nr. flavus against citricola scale. At both field sites, (Lindsay and Porterville, CA) parasitoid releases were associated with significantly reduced scale populations. Thus, the data confirm that M. sp. nr. flavus is a promising biological control agent of citricola scale.

A major reason for the success of M. sp. nr. flavus may be that this parasitoid can exploit small scales for host feeding. Even though these small scales which are killed through host feeding cannot be used for reproduction, host feeding will increase the longevity of the adult parasitoids. Hence, adult females can survive until scales are big enough to be parasitized. The ability to exploit small scales is a critical feature of the biology of this parasitoid because a single synchronized generation of citricola scale per year results in an extended time period when only small scales are present.

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