Antennal olfactory receptor neurons (ORNs) for pheromone and plant volatile compounds were identified and characterized in Sitona lepidus and S. discoideus, using the single sensillum recording technique with five pheromone-related compounds and 40 host and non-host plant volatile compounds. Different types of olfactory sensilla containing specialized ORNs were identified in these weevils. Different types of sensilla housed ORNs specialized for pheromone-related compounds, 4-methyl-3,5-heptanedione or one or more of four stereoisomers of 5-hydroxy-4-methyl-3-heptanone. In addition to the pheromone-related ORNs, several types of olfactory sensilla contained ORNs responsive to plant volatile compounds. Most of the ORNs showed high specificity to specific volatile compounds although some of the active compounds showed overlapping response spectra in the ORNs across different types of sensilla. Our study indicates that both S. lepidus and S. discoideus have species-specific set of highly sensitive and selective ORNs for pheromone and plant volatile compounds. The behavioral implication of these findings is discussed.

• Kye Chung Park(New Zealand Institute for Plant and Food Research, New Zealand)
• Rikard Unelius(Linnaeus University, Sweden)
• Mark McNeill(AgResearch, New Zealand)