The effects of bait applications on the overall activity of the Formosan subterranean termite, Coptotermes formosanus Shiraki, in a town of 1.2 km² were assessed between 2001 and 2003 by using a bait impact index. The index incorporated the amount of baits applied and the distance between bait application loci and the monitoring stations from which termite activity was measured. Even with the collaboration of only 35% of the residents and incomplete treatment records, the bait impact index demonstrated that more baits applied in proximity to monitoring loci significantly caused the decline of C. formosanus activity.