Odorant capture: heterogeneity of cuticular lipid coatings on moth trichoid sensilla

The lipid coatings on trichoid sensilla of male moths may be involved in both the selective adsorption of pheromone molecules from the air, as well as focusing these molecules onto sensillar pores. We found that in Helicoverpa zea moths, there were in fact significant differences in the lipids on male antennae compared to those of females and these could be attributed to the males’ trichoid sensilla. Thus at the macro-level we found evidence for differential coating of trichoid sensillar surfaces that might selectively adsorb H. zea aldehyde pheromone molecules. We then used atomic force microscopy (AFM) on the sensilla to determine their individual nano-terrains, followed by chemical force microscopy (CFM) to contact the surfaces and probe for differences in chemical bonding forces that could indicate differences in lipid coatings on different local sensillar regions. Using a hydrophilic CFM silica tip, we found that H. zea trichoid sensilla exhibited heterogeneity in their lipid coatings, with the multitudes of ridges on each sensillum possessing more hydrophobic coatings than the pore-containing areas. These results suggest that there is a lipid-based nano-focusing of the aldehyde pheromone molecules into the pores from non-pore-containing areas of the sensilla. A second species, Utethesia ornatrix, which uses hydrocarbon pheromone components and not aldehydes, exhibited no lipid heterogeneity on its trichoid sensillar surfaces when the hydrophilic CFM tip was used. These findings suggest that the mechanisms of adsorption of the aldehyde- versus the hydrocarbon-based pheromone components on the sensilla of these two species are different.