The tobacco cutworm, Spodoptera litura, is a globally important agricultural pest that relies on a female-produced sex pheromone blend for mate location. Here, we investigated the electrophysiological and behavioral responses of S. litura to its sex pheromone components and structurally related compounds using gas chromatography–electroantennogrm detection (GC-EAD) and field trapping assays. Most of the 17 compounds tested elicited antennal responses in both sexes, although response magnitude and sensitivity differed markedly among compounds and between males and females. Male responses were generally stronger, but females also detected several pheromone-related compounds with high sensitivity, demonstrating previously unrecognized pheromone autodetection in S. litura. In field assays, four compounds, Z7-12:Ac, Z9-14:Ac, Z9-14:OH, and Z9E12-14:Ac, strongly inhibited male attraction to the conspecific pheromone. Other structurally related compounds either had weaker or inconsistent inhibitory effects. Our findings suggest that broad sensitivity to structurally related and heterospecific pheromone compounds may contribute to discrimination among chemically similar odor signals and thereby facilitate species recognition and reproductive isolation in Spodoptera. The potent behavioral antagonists identified here also provide promising candidates for the development of pheromone-based, environmentally sustainable approaches to S. litura management.