Electrophysiological responses of Cydia pomonella to codlemone and pear ester ethyl (E,Z)-2,4-decadienoate: peripheral interactions in their perception and evidences for cells responding to both compounds

Electroantennography (EAG) recordings were made from both virgin and mated males and females of Cydia pomonella (L.) (Lepidoptera Tortricidae) (CM) on stimulation with the main component of its sex pheromone (E,E)-8,10-dodecadien-1-ol (E8E10-12:OH) and ethyl (E,Z)-2,4-decadienoate (Et-2E,4Z-DD), a ripe pear-derived volatile attractant. CMs of 7 Italian populations collected on different host-plants (3 apple, 3 walnut, 1 pear) were used. The dose-response curves to the volatile compounds (9 doses) were calculated and differences in olfactory sensitivity of virgin and mated males and females of the different populations are discussed. As expected, females were much less sensitive than males to E8E10-12:OH but generally showed a similar response to the higher doses of Et-2E,4Z-DD. EAG amplitudes were not significantly different among virgin and mated adults, as well as between two populations collected in a chemical treated apple orchard and an organic farm, respectively. The males of the walnut populations showed a lightly higher sensitivity to E8E10-12:OH. Differential saturation experiments (DS-EAG) showed that the antennae of C. pomonella clearly reduce their response to Et-2E,4Z-DD when continuously stimulated with E8E10-12:OH. Recordings from single antennal olfactory cells SCR showed the presence of cells responding only to E8E10-12:OH or Et-2E,4Z-DD but also to the 2 compounds. During field tests, all doses of Et-2E,4Z-DD showed an attractant activity on both sexes of CM. A synergistic effect on male attraction was not observed by adding Et-2E,4Z-DD to the pheromone; nevertheless, a clear interference on pheromone trap efficiency was detected. These observations have to be highly considered when setting up mixtures of E8E10-12:OH and Et-2E,4Z-DD to monitor codling moth populations.