Philodendron adamantinum(Araceae) lures its single cyclocephaline scarab pollinator with specific dominant floral scent volatiles

Abstract

Cyclocephline scarabs and their host plants are documented as highly specialized plant–pollinator associations, with various fine-tuned adaptations. We studied the association between Philodendron adamantinum, a species endemic to the Espinhaço Range in Minas Gerais, South-East Brazil, and its exclusive pollinators. We focused on the pollination mechanism and reproductive success of P. adamantinum, analysed its floral scent composition, and performed field bioassays to verify the scent-mediated attraction of pollinators. The reproductive success of P. adamantinum depends on the presence of Erioscelis emarginata (Scarabaeidae, Cyclocephalini), its sole pollinator. At dusk, the inflorescences heat up to 18 °C above the surrounding ambient air temperature and give off a strong sweet odour, from which 32 volatile compounds were isolated. Dihydro-β-ionone, the major constituent in the floral scent bouquet, lures individuals of E. emarginata when applied to scented artificial decoys, either alone or blended with methyl jasmonate. We attribute the low fruit set of P. adamantinum at our study sites to pollinator limitation of small and isolated populations and geitonogamic pollen flow of vegetatively generated clonal plant groups. The interaction between P. adamantinum and E. emarginata shows common traits typical of the known plant–pollinator associations involving cyclocephaline scarabs: the asymmetrical dependence of plants on their pollinators, and the scent-mediated interaction between flowers and beetles. In addition to updating the current catalogue of active compounds of cantharophilous pollination systems, further experimental studies should elucidate the role of the specific chemical compounds that attract pollinators along different time and biogeographic scales.