In pheromone-based surveys for detecting multiple species of exotic lymantriine moths (Lepidoptera: Noctuidae: Lymantriinae), spacing between traps baited with species-specific pheromone lures must be sufficient to prevent antagonistic effects of heterospecific pheromone on lure attractiveness. Conducting field experiments with the Japanese gypsy moth, Lymantria dispar japonica Motschulsky, in northern Honshu, Japan, we first determined which congeneric pheromone components have strong antagonistic effects on attraction of male moths to the conspecific pheromone (7R,8S)-cis-7,8-epoxy-2-methyloctadecane (( )-disparlure). Since the most antagonistic compounds were pheromone/volatile components from the sympatric nun moth, L. monacha (L.), we then conducted experiments with paired traps baited with either a L. dispar (L.) pheromone lure (( )-disparlure (50 µg)) or L. monacha pheromone lure (a mixture of (7R,8S)-cis-7,8-epoxyoctadecane (( )-monachalure (50 µg)), (7Z)-2-methyloctadecene (5 µg), and ( )-disparlure (50 µg)). As spacing between paired traps increased (0, 0.5, 2, 7.5, 15, or 30 m), the antagonistic effect of the L. monacha lure on the attractiveness of the L. dispar lure decreased and finally disappeared. For pheromone-based detection surveys of multiple species of exotic lymantriine moths in North America to be effective, trap spacing of 15 m is recommended.