Interspecific Variation of Floral Scent Composition in Glochidion and its Association with Host-specific Pollinating Seed Parasite (Epicephala)

Abstract

Trees of the genus Glochidion (Phyllanthaceae) are pollinated by females of Epicephala moths (Gracillariidae) whose larvae consume the seeds of the flowers that they pollinate. Each Epicephala moth species is specific locally to a single host species, although two to four Glochidion hosts often cooccur. To investigate the role of olfactory signals in maintaining the plant-moth specificity, we analyzed floral scent composition of five Glochidion species by using gas chromatography-mass spectrometry (GC-MS) and conducted Y-tube olfactometer bioassays with Epicephala moths and their host flowers. The GC-MS analysis showed that the floral scents of the five Glochidion species are dominated by (R)-(-)- and (S)-(+)-linalool, and (E)- and (Z)-beta-ocimene, and that each species produces 6-20 compounds. Transformation of scent profiles by using chord-normalized expected species shared distances and analysis of the data with nonmetric multidimensional scaling showed that floral volatiles of cooccurring Glochidion species can be distinguished by relative chemical composition, especially that of minor compounds. The bioassay with pollinators of Glochidion lanceolatum and Glochidion ruburm further indicated that Epicephala moths are capable of discriminating their hosts by using floral odor. The results suggest that the floral scent of Glochidion is one of the important key signals that mediate the encounters of the species-specific partners in the Glochidion-Epicephala mutualism.