Pollination of Diuris maculata (Orchidaceae) by male Trichocolletes venustus bees

In a previous study, the Australian terrestrial orchid Diuris maculata sensu lato, from a site near Melbourne in Victoria, was suggested to be a floral mimic of several sympatric legume species. The widespread distribution of this orchid species (or species complex) suggests that there may be a number of different model and pollinator species throughout this range, and that additional studies are necessary to characterise its pollination adequately. In this study, the pollination of D. maculata in the Sydney region, mainly at Scheyville National Park, was compared with the results previously obtained in Victoria. At Scheyville National Park, Trichocolletes venustus was the only native bee species found in significant numbers, and the flowers it visited were almost exclusively the legumes Hardenbergia violacea and Daviesia ulicifolia ssp. ulicifolia. Fifty per cent (14 of 28) of captured male bees carried D. maculata orchid pollinaria, or remnants, which were identified by AFLP fingerprinting. Female bees, which appeared about 10–14 days after males, were not observed visiting the orchid or carrying orchid pollinaria. We confirmed that D. maculata flowers lack nectar, and noted that the pea-like flowers possess an UV false nectar guide comparable to the true UV nectar guide of the legume flowers. Colorimetric analysis showed the colour separation between D. ulicifolia ssp. ulicifolia and the orchid is small enough to be likely to produce foraging errors, consistent with mimicry. We conclude that guild mimicry of a diversity of ‘egg and bacon’ legumes best explains the pollination of D. maculata s.l., rather than precise mimicry of any one pea species. Preliminary observations suggest that pea-flower mimicry may range from being highly precise in some species, through to being much more generalised, but still retaining elements of mimicry. The novel finding of comparable UV patterns in Diuris species and putative pea models applies to most species in the genus and we found that the rare D. aequalis shows remarkable similarity in colour, shape and UV patterns to the sympatric legume Gompholobium huegelii, and is likely to be a mimic of this species.