The nursery pollination mutualism between Epicephala moths (Gracillariidae) and trees of the genera Glochidion, Phyllanthus and Breynia (Phyllantheceae) was discovered less than a decade ago. In contrast to yuccas, these plants are monoecious, producing separate male and female flowers. Thus, possible sexual dimorphism in floral traits such as scent production could be a mechanism in these plants to induce distinct behaviours in female moths, i.e. pollen collection on male flowers, and pollen deposition and oviposition on female flowers.
In collaboration with Prof. Makoto Kato and coworkers (Kyoto University, Japan). and Prof. Atsushi Kawakita at Kyoto University (Japan), I have analysed the floral scent chemistry of Breynia vitis-idea, which is distributed from Pakistan to Southern Japan. Odour collection was performed on several islands in the Ryukyu Archipelago in Japan.
As predicted, I found a clear sexual dimorphism in floral scent in this plant. Two compounds, 2-phenylethyl alcohol and 2-phenylacetonitrile, which are abundant in both floral types, make up the attractive blend for female moths. Interestingly, these compounds have been identified as floral compounds in many flowering plants, showing that these very specialised insect-plant interactions are not necessary mediated by specialised floral chemistry.
Picture: Yellow male ﬂowers and green female ﬂowers arranged at the base and at the apex, respectively, of a branch of Breynia vitis-ideae. Ishigaki Island, Japan. Photo: Glenn Svensson.