Anther mimicry in an African orchid pollinated by pollen-feeding beetles

Flowers of many species have yellow markings that appear to mimic anthers or pollen and attract the attention of pollen-seeking insects (usually female bees). We investigated a putative case of anther mimicry in Disa similis, an orchid with nectarless mauve flowers and conspicuous yellow markings on the tips of the labellum and lateral petals. We studied D. similis in grasslands of KwaZulu-Natal, South Africa, by directly observing floral visitors. Spectral reflectance of floral parts of the orchid and sympatric species were analysed using spectrometry. Pollination success was recorded in relation to colour manipulation and florivory of the petal apices. Overall pollen transfer efficiency and breeding system was estimated to determine pollinator dependence for fruit set. The flowers of D. similis lack scent and are pollinated by the pollen-feeding beetle Isoplia lasiosoma which chews on the yellow petal apices. Overall flower colour resembles that of co-flowering plants that are visited by beetles for pollen-feeding, and the yellow UV-absorbing colour of the petal apices matches that of anthers and pollen. By covering the yellow markings with purple paint or removing them led to reduced pollination success. Pollen removal and deposition were strongly associated with florivory. Plants are self-compatible and dependent on pollinator visits for fruit set. Previous studies of orchids and other plants that deploy mimicry of anthers and pollen have reported bees or flies as pollinators without physical damage to flowers. Pollination of D. similis by pollen-feeding beetles and their consumption of anther-like apices of the petals are thus unexpected and novel findings.