Floral specialization for beetle pollination and its implications for pollen dispersal in an African orchid

Pollination by beetles is relatively rare in orchids, and this has been attributed to the clumsy behavior of beetles being unsuitable for the precise pollen transfer mechanisms that characterize the orchid family. We investigated floral specialization for beetle pollination in the rare fire-dependent South African orchid Disa elegans and explored its implications for the efficiency and spatial pattern of pollen dispersal.

We observed flower visitors and identified their pollen loads. We studied floral traits, including spectral reflectance patterns, nectar secretion, and scent chemistry. We tracked the dispersal of color-labeled pollen.

Disa elegans was found to be pollinated by large scarab beetles. Apparent floral adaptations for beetle pollination include the platform-like corymbose inflorescence of upward-facing, bowl-shaped flowers, secretion of very dilute nectar on exposed surfaces of the petals, and fruity floral scent dominated by the monoterpene alcohol R-(-)-β-linalool and benzenoid ester methyl benzoate. Beetles carry large loads of pollinaria and transfer ~13% of the pollen they remove from anthers to stigmas. We found a classic leptokurtic kernel of pollen dispersal with an average distance from donors to recipients of 6.7 m. Self-pollen made up ~30% of all pollen deposited on stigmas by beetles. These pollen dispersal patterns are similar to those obtained in plants pollinated by other insect groups, such as bees.

These results provide evidence of floral specialization for beetle pollination in an orchid species and show that beetles can be effective agents of pollen dispersal in orchid populations.