Nursery, Greenhouse, and Landscape News

Chilocorus kuwanae Suppressing Euonymus Scale

The lady beetle Chilocorus kuwanae was the first natural enemy introduced for control of euonymus scale as part of a USDA program from the early 1980's through 1995. Beetles of Korean origin had been established in the Washington, D.C. area by 1984, but they did not do well in southern New England. Suspecting that the Korean populations were not well adapted to the colder winters of New England, adults bred from beetles collected in China were released and became established. This Chinese strain was widespread throughout southern New England by 1994.

But what effect would the beetle have on euonymus scale populations? To assess the effectiveness of C. kuwanae in reducing euonymus scale, 27 sites with one or more moderately to heavily infested euonymus shrubs were chosen as study sites in Massachusetts, Connecticut, and Rhode Island. Beetles were released repeatedly at 14 of the sites until a breeding population was established. No beetles were released at the other 13 sites. In addition, observations were made for 5 years at a 79-acre apartment complex in the greater Boston area that contained about 110 widely dispersed euonymus plants. A release of 50 adult beetles was made in May 1991 and shrubs were examined every fall until 1995.

C. kuwanae suppressed euonymus scale at 9 of the 14 release sites. Beetle establishment was best at sites with heavily infested shrubs in sunny locations. The beetle failed to establish large populations at 3 sites (shady sites or with few scales present), and 2 sites had to be abandoned when the shrubs were removed by the owners (scale populations exceeded the owner's tolerance for aesthetic damage before beetle populations could suppress the scales).

The beetle has rapidly spread on its own after release. Of the 13 check sites, 9 were invaded by C. kuwanae during the experiments. The beetle became abundant at 3 locations, resulting in a decline in scale numbers.

At the apartment complex, C. kuwanae spread to 64% of all euonymus plants within 4 months and the proportion of plants with heavy euonymus scale infestations decreased from 46 to 13% within 1 year. This ability to suppress heavy scale infestation to lower levels is of economic value because plant survival is reduced only by heavy scale infestations.

Source:

Van Driesche, R., K. Idoine, M. Rose and M. Bryan. 1998. Evaluation of the effectiveness of Chilocorus kuwanae (Coleoptera: Coccinellidae) in suppressing Euonymus scale (Homoptera: Diaspididae). Biol. Control 12: 56-65.


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