Betula pendula Roth is a popular ornamental tree in northern California, which frequently hosts populations of four leaf-feeding aphid species. Differential aphid species distribution on occasional birch trees led to the identification of Betula pubescens Ehrhart, a closely related species, planted among B. pendula. Spring sampling demonstrated that Calaphis flava Mordvilko occurred predominantly on B. pubescens while Betulaphis brevipilosa Borner, Callipterinella calliptera (Hartig), and Euceraphis betulae (Koch) were more abundant on B. pendula. C. calliptera and E. betulae were rarely found on B. pubescens , whereas C. flava populations constituted 22% of the aphid fauna on B. pendula when trees of the two species were adjacent. B. pubescens hosted a larger total aphid population as well as abundant leafhoppers. Honeydew presence on lower canopy leaves of both tree species was positively related with aphid density.