Can pollen headspace volatiles and pollenkitt lipids serve as reliable chemical cues for bee pollinators?

Chemical analysis of putative contact chemical cues for pollinators from pollen of two plant species, Ranunculus bulbosus (Ranunculaceae) and Campanula rapunculoides (Campanulaceae), showed high consistency in the qualitative and quantitative composition of pollenkitt surface lipids in all samples analyzed per species. The pollenkitt lipids of R. bulbosus included an aldehyde, fatty acid amides, saturated and unsaturated hydrocarbons, and secondary alcohols; the lipids of C. rapunculoides consisted of an aldehyde, monoketones, and β-diketones. In marked contrast, the pollen headspace volatiles showed a wide qualitative and quantitative variability among all samples per species, whereby the variability was more pronounced in R. bulbosus. Hence, the highly species-specific pollenkitt lipids may provide pollinators with more reliable information on pollen identity.