Iridoid Sex Pheromone Biosynthesis in Aphids Mimics Iridoid‐Producing Plants

Biosynthesis of (1 R ,4a S ,7 S ,7a R )‐nepetalactol ( 1 ) and (4a S ,7 S ,7a R) ‐nepetalactone ( 2 ) in plants involves iridoid synthase (ISY), an atypical reductive cyclase that catalyses the reduction of 8‐oxogeranial into the reactive enol of ( S )‐8‐oxocitronellal, and cyclization of this enol intermediate, either non‐enzymatically or by a nepetalactol‐related short chain dehydrogenase enzyme (NEPS) that yields the nepetalactols. In this study, we investigated the biosynthesis in vivo of 1 and 2 in the pea aphid, Acyrthosiphon pisum , using a library of isotopically‐labelled monoterpenoids as molecular probes. Topical application of deuterium‐labelled probes synthesized from geraniol and nerol resulted in production of 2 H 4 −lactol 1 and 2 H 4 −lactone 2 . However, deuterium incorporation was not evident using labelled probes synthesized from ( S )‐citronellol. These results suggest that iridoid biosynthesis in animals, specifically aphids, may follow a broadly similar route to that characterised for plants.