Aromatic Volatiles and Odorant Receptor 25 Mediate Attraction of Eupeodes corollae to Flowers

Flowering plants attract pollinators with volatile chemicals that include aromatic compounds. Syrphid flies are the largest group of flower visitors in Diptera, but little is known about how they detect floral scents at the molecular level. Here, electroantennogram (EAG) recordings from the antennae of Eupeodes corollae were used to measure responses from 14 aromatic compounds. To identify odorant receptors (ORs) of E. corollae tuned to aromatic volatiles, we analyzed functional profiles of Drosophila melanogaster odorant receptors (ORs), DmelOR46a and DmelOR71a, which are narrowly tuned to phenolic compounds and represent the orthologues of E. corollae OR25 and OR28, respectively. The two genes that are expressed in the antennae of both sexes were functionally characterized. EcorOR25 is narrowly tuned to several structurally related floral scent volatiles, including eugenol, p-cresol, and methyl eugenol. Finally, choice behavior assays showed that eugenol and methyl eugenol were attractants for both sexes of E. corollae adults. This study identified the odorant receptors used by E. corollae to detect aromatic volatiles, suggesting environmentally friendly strategies to attract these beneficial insects.