Neuroethology of pheromone-plant odour interaction in the codling moth

Revealing the mechanisms underlying the coding of odour mixtures is an outstanding challenge in olfactory neuroethology. By using a multimodal approach, including behavioural analysis, optical imaging of the primary olfactory centre, the antennal lobe (AL), and intracellular recordings of AL neurons, we studied how binary blends of the main pheromone component (codlemone) and three plant volatiles affected the behaviour and odour processing in the codling moth Cydia pomonella. In wind tunnel bioassays, males of C. pomonella were more attracted by the blends than by the single components. Optical imaging revealed that the presence of the plant volatile enhanced the response to a suboptimal dose of codlemone in the large pheromone-tuned glomerulus, the cumulus (Cu), while additive and suppressive interactions were observed in other areas of the AL. Intracellular recordings from projection neurons confirmed that the synergistic responses were confined to the Cu and some glomeruli in the macroglomerular complex. Hence, we demonstrate that behaviourally active blends of sex pheromone and host plant volatiles have a synergistic effect in the pheromone subsystem of the codling moth AL. Our physiological analysis suggests that this interaction may occur already at the peripheral olfactory level or as a result of presynaptic modulatory mechanisms.