Dispensers of E8,E10-12OH (codlemone), E8,E10-12Ac (codlemone acetate), or both dispenser types were placed on the corners of 100 m(2) and 300 m(2) plots within apple orchards. Communication disruption of male codling moths, Cydia pomonella, was monitored with pheromone traps in the centres of these plots. In the 300 m(2) plots, trap catch was reduced only by codlemone. In the 100 m(2) plots, trap catch was reduced in all three treatments, fewest males were caught in plots treated with both codlemone and codlemone acetate. Males were attracted to codlemone dispensers, they were also flying actively around the tree crowns, well above the dispensers. This behaviour was not observed in treatments with codlemone acetate, where male orientation flights were directed only towards the trap in the plot centre. The antagonistic effect of each of the four geometric isomers of codlemone acetate was shown by another trap test. Addition of 20% E,E-; E,Z-; Z,E- or Z8,Z10-12Ac decreased male attraction to traps baited with E8, E10-12OH.