Generalised pollination of Diuris alba (Orchidaceae) by small bees and wasps
Most Diuris species possess flowers of pea-like form and colour, and occur in association with flowering peas of the tribe Mirbeliae. Previous studies of the pollination of Diuris maculata sensu lato have found evidence for guild mimicry of pea flowers. The flowers of Diuris alba are also pea-like in form but not in colour, and this species is frequently found in habitats where peas are uncommon or absent. We investigated the pollination of Diuris alba, which we expected may have a distinct pollination system at Lake Munmorah, New South Wales. Many Diuris species lack floral rewards, but D. alba produced a small amount of nectar. Flower visitors, and hence putative pollinators, were mainly female Exoneura bees, but also the wasps Eurys pulcher and a Paralastor species. Reproductive success of D. alba, both in woodland containing abundant Dillwynia retorta and in heathland where this pea was absent, was higher than in the previously studied D. maculata s.l. We suggest that the pollination of D. alba is more generalised than that found in the legume guild mimic D. maculata s.l. Although its flowers may display structural similarity to pea flowers, other characteristics suggest that its pollination system has diverged from a presumed pea-mimicry ancestral condition.