New Potential Inhibitors of Pheromonal Attractionin the Oriental Fruit Moth, Cydia molesta

New analogues of (Z)-dodec-8-en-1-yl acetate (Z8-12:OAc, 1), the main sex pheromone component of the Oriental fruit moth, Cydia molesta, were designed by formally transferring the terminal propyl group from the C-9 to the C-7 position to form vinyl-branched (2, 3) or, after isomerization, ethylidene-branched (4) structures and by replacing the -CH=CH- grouping by the -S-CH2- moiety (5, 6). Their biological activities were studied both electrophysiologically and behaviourally (laboratory mating and wind tunnel experiments). All the structural modifications resulted in analogues whose electroantennographic activities were lower than that of 1 following the order 1 >> 6 ≈ 5 >> 2 ≈ 4 ≈ 3. The single sensillum recording activities indicated that all the analogues stimulate the same Z8-12:OAc receptor neurone. In behavioural experiments, the analogues were generally found to reduce the ability of males to find a pheromone source, however, to different degrees. The highest inhibitory effect (90%) was observed for the thia analogues 5 and 6. The results support the view that the inhibitory properties of the analogues should not be entirely associated with their pheromone-mimicking capabilities.