The electrophysiological and behavioral responses of maleAgrotis segetum to fluorinated analogs of (Z)-5-decenyl acetate (Z5-10∶OAc) were investigated. The single sensillum recordings showed that 4,4-difluoro-(Z)-5-decenyl acetate (4,4-F2), 7,7-difluoro-(Z)-5-decenyl acetate (7,7-F2), 10,10,10-trifluoro-(Z)-5-decenyl acetate (10,10,10-F3) and 7,7,8,8-tetrafluoro-(Z)-5-decenyl acetate (7,7,8,8-F4) were each 100-fold less active than the natural Z5-10 ∶ OAc, whereas the 7,7,8,8,9,9,10,10,10-nonafluoro-(Z)-5-decenyl acetate (F9) analog was essentially inactive. A mixture of Z5-10 ∶ OAc, Z7-12 ∶ OAc, and Z9-14 ∶ OAc on a filter paper dispenser was as attractive as female gland extracts when tested in a flight tunnel. With Z5-10∶OAc omitted, the two-component mixture elicited a significantly lower male response. Four analogs, 7,7-F2, 10,10,10-F3, 7,7,8,8-F4, and F9, were added separately to the two-component mixture to replace Z5-10∶OAc. The responses elicited by the mixtures containing the 7,7-F2, 10,10,10-F3, and 7,7,8,8-F4 analogs did not differ significantly from that of the natural three-component mixture and the two-component mixture, whereas the mixture containing F9 elicited a significantly lower male response, as low as the response to the two-component mixture. In a field test the mixtures containing 10,10,10-F3 and 7,7,8,8-F4 were significantly more active than the two-component mixture, but still less active than the natural three-component mixture. It appears that field tests provided greater discrimination among pheromone analogs in assessing their behavioral activity than the flight-tunnel test did. Structure-activity analyses demonstrate the importance of the lipophilic interaction between the terminal alkyl chain and the receptor site for the activity of the stimulus. The lipophobicity of the fluorinated analogs impedes a productive receptor interaction.