The general odorant-binding protein 2 of Mamestra brassicae males has been purified from antennal extracts and examined in binding assays with pheromone components of this species and a behavioral antagonist, cis-11-hexadecenol. The protein showed high affinity for the latter compound and no affinity for the pheromone components. In addition, expression of the protein, studied by in situ hybridization, was restricted to the long sensilla trichodea, which house the neuron that responds to cis-11-hexadecenol. The expression in a functionally defined population of sensilla, together with binding specificity and previous electrophysiological data, suggest an unsuspected role for the general odorant-binding protein 2 in M. brassicae. It may be involved in the transduction process for the behavioral antagonist to which neurons are specifically tuned and always cocompartmentalized in long trichodeal hairs, with neurons responding to the major pheromonal compound, cis-11-hexadecenyl acetate. These data are consistent with the involvement of odorant-binding proteins in the fine discrimination between pheromone and antagonist, which is related to avoidance of interspecific mating mistakes.