ABSTRACTIn field‐trapping experiments the unsaturated analogues (E)‐6‐, (E)‐12‐, and (Z)‐12‐tetradecenyl acetate were as attractive to maleYponomeuta rorellusLatr. as the native pheromone component tetradecyl acetate. All four analogues attracted more males than virgin females did, whereas (Z)‐6‐, (E)‐11‐, (Z)‐10‐ and (Z)‐11‐tetradecenyl acetate were essentially non‐attractive. Addition of 1–30% of (Z)‐11‐tetradecenyl acetate to the pheromone tetradecyl acetate reduced the attraction to less than 2%. Flight tunnel experiments withY. rorellusconfirmed the activity of the (E)‐6‐ and (E)‐12‐tetradecenyl acetates and demonstrated the activity of (E)‐7‐tetradecenyl acetate as well. These analogues elicited orientation behaviour, upwind flight and landing at the odour source as frequently as the native pheromone did. Single sensillum recordings from maleY. rorellusshowed two types of cells in most sensilla. A large spike amplitude cell was stimulated by tetradecyl acetate and the unsaturated analogues (E)‐11‐, (E)‐6‐ and (E)‐12‐tetradecenyl acetate, and to a lower extent by the (Z)‐6‐, (Z)‐11‐ and (Z)‐12‐isomers. A cell with medium spike amplitude was stimulated by (Z)‐9‐tetradecenyl and (Z)‐11‐hexadecenyl acetate. Some sensilla contained a third cell firing with a small spike amplitude which was activated by (Z)‐11‐tetradecenol. Thus the tetradecyl acetate receptor was stimulated not only by the behaviourally active analogues, but also by behavioural antagonists. The interaction of (E)‐11‐tetra‐decenyl acetate and tetradecyl acetate with the same antennal receptor cell was also demonstrated inY.cagnagellus. Electrophysiological discrimination between behavioural attractants and antagonists and the role of behavioural antagonists in the i