Generalized food deception: colour signals and efficient pollen transfer in bee-pollinated species ofEulophia(Orchidaceae)

Abstract

Non-rewarding plants use a variety of ruses to attract their pollinators. One of the least understood of these is generalized food deception, in which flowers exploit non-specific food-seeking responses in their pollinators. Available evidence suggests that colour signals, scent and phenology may all play key roles in this form of deception. Here we investigate the pollination systems of five Eulophia spp. (Orchidaceae) lacking floral rewards. These species are pollinated by bees, notably Xylocopa (Anthophorinae, Apidae) or Megachile (Megachilidae) for the large-flowered species and anthophorid (Anthophorinae, Apidae) or halictid (Halictidae) bees for the small-flowered species. Spectra of the lateral petals and ultraviolet-absorbing patches on the labella are strongly contrasting in a bee visual system, which may falsely signal the presence of pollen to bees. All five species possess pollinarium-bending mechanisms that are likely to limit pollinator-mediated self-pollination. Flowering times extend over 3–4 months and the onset of flowering was not associated with the emergence of pollinators, some of which fly year round. Despite sharing pollinators with other plants and lacking rewards that would encourage fidelity, the Eulophia spp. exhibited relatively high levels of pollen transfer efficiency compared with other rewarding and deceptive orchids. We conclude that the study species employ generalized food deception and exploit food-seeking bees. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 171, 713–729.