A new pheromone antagonist of the codling moth Cydia pomonella is reported. Presaturation of the antennae of the insects with vapors of the antagonist (E,E)-8,10-dodecadienyl trifluoromethyl ketone, analogue of the main component of the pheromone (codlemone), resulted in lower electrophysiological responses to the pheromone relative to untreated insects. In the wind tunnel, the compound elicited a remarkable disruptive effect on all types of behavior of males flying toward a source baited with a pheromone/antagonist blend in 1:1, 1:5, and 1:10 ratios. The insects displayed erratic flights in the presence of the antagonist, as shown by their flight parameters in comparison to insects attracted to the pheromone alone. In the field, traps baited with mixtures of 1:10 codlemone/antagonist attracted considerably lower numbers of males than the natural attractant. The antagonist, however, did not inhibit the pheromone-degrading enzymes present in male antennae, suggesting that trifluoromethyl ketones are not sufficiently electrophilic to produce a stable intermediate adduct with a cysteine residue of the enzyme, a mechanism previously proposed for oxidase inhibition in insects. Overall and taking into account our previous reports and, particularly, the reduction in damage induced in maize fields by a trifluoromethyl ketone analogue of the pheromone of Sesamia nonagrioides (Sole, J.; Sans, A.; Riba, M.; Rosa, E.; Bosch, M. P.; Barrot, M.; Palencia, J.; Castella, J.; Guerrero, A. Reduction of damage by the Mediterranean corn borer, Sesamia nonagrioides , and the European corn borer, Ostrinia nubilalis , in maize fields by a trifluoromethyl ketone pheromone analog . Entomol. Exp. Appl. 2008, 126, 28-39), the antagonist might be a new candidate to consider in future strategies to control the codling moth.