Raupp, M.J., Holmes, J.J., Sadof, C.S., Shrewsbury, P.M., & Davidson, J.A. 2001 Effects of cover sprays and residual pesticides on scale insects and natural enemies in urban forests.. Journal of Arboriculture 27(4): 203-214.

Notes: Trees in residential landscapes that received three cover sprays annually for at least four years harbored a greater diversity of scale insect pests and were much more likely to be infested with scales than trees in landscapes treated with cover sprays for shorter periods of time. Oak (Quercus palustris trees in an institutional landscape treated with residual insecticides harbored significantly lower numbers of beneficial arthropods than trees treated with a pesticide that lacked residual activity. The suppressive effect of residual insecticides on natural control was pronounced on the community of parasitic wasps that attack the obscure scale (Melanaspis obscura), a common scale insect pest of oak. Other species discussed include Chionaspis pinifoliae, Fiorinia externa, Lepidosaphes beckii, Parthenolecanium corni and Planococcus citri.