Three species of autoecious aphids, Callipterinella calliptera (Hartig), Euceraphis betulae (Koch), and Betulaphis brevipilosa Börner, commonly occur on European white birch trees, Betula pendula Roth, in northern California. Populations were sampled from 1981 through 1984 at two sites. Within-tree populations of all three species were more abundant in the lower and middle vertical thirds of tree canopies. Optimal sample sizes were estimated for individual trees as well as tree populations, given variable mean aphid densities, sampling reliability levels, and sampling costs. An aesthetic injury level for honeydew production was estimated.
