To effectively monitor forest tent caterpillar (Malacosoma disstria Hübner) populations, the use of synthetic sex pheromones to trap adults was evaluated in outbreak and nonoutbreak population levels. Three pheromone blends were field-tested, consisting of 1) (Z,E)-5,7-dodecadienal, 2) 100:1 (Z,E)-5,7-dodecadienal: (Z,Z)-5,7-dodecadienal and 3) 100:1:10 (Z,E)-5,7-dodecadienal: (Z,Z)-5,7-dodecadienal: (Z)-7- dodecanal. The tertiary blend (3) was superior for capturing forest tent caterpillar moths, and was best able to resolve population density levels. Lures dosed with 11 μg or less of either the binary (2) or tertiary blends failed to capture moths at nonoutbreak population levels, while lures dosed at 390 μg gave the highest mean trap catch and the lowest rate of zero-captures.