Temporal variation in floral scent emission of a woody plant and flower visiting behaviour of male and female flies

Most flowering plants rely on insects for pollination and flowers are advertised using odor and visual cues. Flower scent consists of a complex blend of volatile compounds of which the emission can vary over time (and space) within species. Pollinator foraging behaviour, such as the choice for flowers and the time spent gathering nectar and/or pollen, can also show significant intraspecific variation. Underlying variation in pollinator behaviour can be sensory or foraging-related biases among sexes or individuals. Investigating the role of temporal variation in floral volatiles on visitation behaviour of male and female pollinators is largely unexplored. We examined temporal variation in the emission of scent of yellowhorn Xanthoceras sorbifolium flowers, visitation behaviour of its main pollinators, male and female Bibio rufiventris flies, and their responses to floral volatile compounds using field experiments and controlled bioassays. Our results show significant daily fluctuations in floral volatile emission of X. sorbifolium in the field. The relative emission of 1-octen-3-ol, 1-octanol, benzaldehyde, and α-farnesene increased from 9:00 to 15:00 h, while (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, (E)-2-hexenal, 2-methyl-6-hepten-1-ol, (E)-2-nonenal, 2,6,6-trimethyl-2-cyclohexene-1-methanol, (E)-2-nonenal, and (E,Z)-2,6-nonadienal decreased. In concert, we observed an increase in visits and visitation duration for male pollinators, but a decrease for female visitation duration. Pollinators exhibited sex-specific responses to floral volatiles, with attraction to 1-octen-3-ol and 1-octanol for B. rufiventris males, while (E)-2-nonenal, (E,Z)-2,6-nonadienal, and (E)-2-hexenal attracted females. Our study shows that temporal variation in floral scent may explain differences in flower visitation by male and female pollinators through sex-specific responses to floral volatiles. Investigating sex-based differences exhibited by pollinators and temporal variation in floral scent emission will help understand the dynamic nature of plant–pollinator interactions.