Pheromone lures for eastern and western blackheaded budworms, Acleris variana (Fernald) and A. gloverana (Walsingham), were synthesized and deployed in traps at locations with decreasing and increasing populations of western blackheaded budworms in British Columbia, Canada. Traps baited with these lures caught comparable numbers of moths at all sites tested in each year. The lures were sensitive to changes in density of budworm populations below observable damage levels, and numbers of moths in traps were strongly correlated with independent estimates of egg densities in the same year. The results confirm the qualitative similarity of the sex pheromones in eastern and western species of blackheaded budworm and demonstrate their utility as a tool for monitoring population trends, including increases in populations to damaging levels.