Multi-season effects of foliar and systemic insecticides on calico scale and their natural enemies

Calico scale (Eulecanium cerasorum) is an exotic pest of shade and ornamental trees and feeds on phloem sap, reduces tree vigor and can ultimately kill trees. We observed effects of four foliar applied (bifenthrin, pyriproxyfen, chlorantraniliprole and cyantraniliprole) and two soil applied pesticides (dinotefuran, imidacloprid) on calico scales and their natural enemies on infested thornless honeylocust trees (Gleditsia triacanthos inermis) over three years. Bifenthrin, dinotefuran and cyantraniliprole provided the largest reductions in scale populations when they were applied to egg laying females on branches early in the season. In contrast, bifenthrin and pyriproxyfen provided the most consistent reductions in scales when they were applied to settled scales on leaves late in the season. None of the insecticides reduced natural enemy abundance when they were applied to target egg laying females early in the season. In contrast, bifenthrin and pyriproxyfen reduced natural enemy abundance when they were applied to settled scales on leaves late in the season. Laboratory assays indicated that foliar applications of bifenthrin were highly toxic to larval Chrysoperla rufilabris (Chrysopidae: Neuroptera), 4 DAT but not 50 DAT.  In contrast, toxicity of pyriproxyfen and chlorantraniliprole were moderately toxic to C. rufilabris at 4 DAT and 50 DAT.  This suggests physiological selectivity of a pesticide and the timing of its application can influence its activity against scales and their natural enemies.