Single-compound floral signaling stabilizes cooperation in an obligate brood-site pollination mutualism

Field bioassays with synthetic stereoisomers showed that (+)-dihydroedulan I elicited stereotypical zigzag odor-tracking flights by female D. heterosmilacicola that closely matched natural orientation toward S. insularis flowers, whereas the diastereomer (-)-dihydroedulan II did not attract the midge. No other insects responded to the baits under field conditions. Together, these findings indicate that a single, stereochemically specific signal shared by both floral sexes reinforces partner fidelity and stabilizes cooperation despite asymmetric larval performance.