Evaluation of the Effectiveness ofChilocorus kuwanae(Coleoptera: Coccinellidae) in Suppressing Euonymus Scale (Homoptera: Diaspididae)

A field experiment on the ability of a Chinese strain ofChilocorus kuwanae(Silvestri) (Coleoptera: Coccinellidae) to suppress densities of euonymus scale (Unaspis euonymi[Comstock]) (Homoptera: Diaspididae) onEuonymusspp. in southern New England was conducted from 1991 to 1995. Observations were made at three spatial scales: (1) a set of 27 sites, 14 of which receivedC. kuwanaereleases and 13 served as checks, (2) a single apartment complex, with approximately 110 euonymus shrubs dispersed over 32 ha, at which a single release was made, and (3) the statewide Massachusetts residential and commercial landscape as a whole.Chilocorus kuwanaesuppressedU. euonymiat 9 of 14 release sites. The beetle failed to establish large populations at three sites, and at two other sites the experiment was ended prematurely by shrub removal by owners. Of 13 check sites, nine were invaded byC. kuwanaeover the course of the experiment and the beetle became abundant at three. Of the 10 check sites whereC. kuwanaeremained absent or rare, scale numbers increased at four locations, decreased at four, and were unchanged at two. At the 32-ha apartment site,C. kuwanaespread 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. At the statewide (MA) landscape level, by 1994 no significant change had yet occurred in the proportion of plants with heavy euonymus scale infestations