In the search for new control methods for the fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), we present the inhibition of the electroantennographic (EAG) response to the pheromone by 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP). As a member of the trifluoromethyl ketones, OTFP is a potent inhibitor of serine esterases, particularly those of insect antennae. Exposure of antennal receptors to OTFP vapors resulted in a decreased amplitude and 2/3 repolarization time (2/3 RT) of the EAG response to the pheromone. The effect was reversible, with the amplitude and repolarization time being recovered upon suppression of the treatment. The non-fluorinated analogue 3-octhylthiopropan-2-one (OTP) did not affect either the amplitude or the 2/3 RT of the EAG response to the pheromone, confirming the key role played by fluorine atoms in this type of chemical. These results may be the basis for new behavioral studies with the aim of considering OTFP in future management strategies of the FAW.