The Spider Orchid Caladenia crebra Produces Sulfurous Pheromone Mimics to Attract its Male Wasp Pollinator

Abstract

One of the most intriguing natural observations is the pollination of orchids by sexual deception. Here, we identify floral semiochemicals from Caladenia (spider orchids) for the first time. We demonstrate that C. crebra, attracts its single pollinator species with a unique system of (methylthio)phenols, three of which are new natural products. Furthermore, the same compounds constitute the sex pheromone of the pollinator, the thynnine wasp Campylothynnus flavopictus, representing the first occurrence of sulfurous sex pheromones in Hymenoptera.

2-(Tetrahydrofuran-2-yl)acetic Acid and Ester Derivatives as Long-Range Pollinator Attractants in the Sexually Deceptive Orchid Cryptostylis ovata

“…10 Additionally, when aliquots of all four extracts were combined on the same pin, no significant enhancement of attraction was achieved (Supporting Information, Table S1). These findings are in contrast to our earlier studies of Australian hammer and spider orchids, 2,23 where using similar methodology we have successfully isolated semiochemicals that induce strong sexual behavior, including frequent attempted copulation at rates similar to that observed with the flowers. For C. ovata, while it is clear that we have successfully isolated long-range pollinator attractants, further work is required to elucidate the missing piece of the puzzle -what triggers pseudocopulation in L. excelsa.…”

“…8,16,17 To date, most studies on the semiochemicals involved in the pollination of Australian orchids have focused on thynnine wasp pollinators. 4,[18][19][20][21][22][23][24] Despite the unusual pollination biology of Australian Cryptostylis, 10,[25][26][27][28][29][30][31] only one study has investigated the chemical signals mediating pollinator attraction. 32 This study by Schiestl et al focused on detecting electrophysiologically active compounds from C. subulata and C. erecta.…”

Breaking the rules: discovery of sexual deception in Caladenia abbreviata (Orchidaceae), a species with brightly coloured flowers and a non-insectiform labellum

“…As such, pollination by a member of the Rhagigasterini suggests that C. abbreviata may well be using a different chemical system to sexually attract its pollinator to those documented for Caladenia species using members of the tribe Thynnini (e.g. Bohman et al 2017;Xu et al 2017). These species have been shown to use (methylthio)-phenols (C. crebra; Bohman et al 2017), and a blend of (S)--citronellol and 2hydroxy-6-methylacetophenone (C. plicata; Xu et al 2017), while pyrazines and chiloglottones are involved in the attraction of sexually deceived thynnine wasps in Drakaea and Chiloglottis respectively (Peakall et al 2010;Bohman et al 2014).…”

“…Bohman et al 2017;Xu et al 2017). These species have been shown to use (methylthio)-phenols (C. crebra; Bohman et al 2017), and a blend of (S)--citronellol and 2hydroxy-6-methylacetophenone (C. plicata; Xu et al 2017), while pyrazines and chiloglottones are involved in the attraction of sexually deceived thynnine wasps in Drakaea and Chiloglottis respectively (Peakall et al 2010;Bohman et al 2014). We predict that exploitation of the Rhagigasterini by Australian sexually deceptive orchids may have been limited by biochemical constraints on the mimicry of the sex pheromones of this group.…”

“…In contrast, the flowers of Caladenia species visited by food-foraging insects tend to be scented, with larger and more colourful flowers (Phillips et al 2009b). While there has been increasing research into the pollination of Caladenia (Phillips et al 2013a(Phillips et al , 2015b(Phillips et al , 2017Swarts et al 2014;Bower 2015;Bohman et al 2017;Reiter et al 2017;Xu et al 2017), some species complexes have received very little attention, particularly those that appear to be dominated by food-deceptive species. This gap in our knowledge of the pollination systems of Caladenia represents a substantial impediment to a better understanding of the evolution of the species diversity and floral traits of this extraordinary genus of orchids.…”