LAUSR

Most studies of angiosperm pollination have been conducted on fully opened flowers, while interactions between animal pollinators and unopened flowers are less well-known. In December 2015, I observed aggregations of small-bodied hylaeine bees swarming between inflexed stamens of unopened blossoms of pink and red flowering gums (Corymbia spp.) planted as municipal street trees in southern New South Wales, Australia (Albury: 36.0737° S, 146.9135° E) (Fig. 1a). The bees appeared to be predominantly Hylaeus (Prosopisteron) perhumilis Cockerell 1914 (expert identification provided via high resolution photographs), but there were also occasionally other small bees from the Halictidae and Colletidae families. All bee visitors appeared to be feeding on pollen-laden anthers. I saw this behavior on more than 15 individual flowers across five trees at various stages of opening between the initial split of the operculum and full extension of stamens. Individual bees were constantly arriving and departing, but a single bud had between 3–7 individuals visiting at any one time. Corymbia ficifolia is native to southwestern Australia, but the species and its hybrids are popular as street trees in urban areas around the country. There is little published empirical work on animal pollination in Corymbia spp., but its pollinators are traditionally assumed to be birds or large-bodied insects (Phillips et al. 2010). The pollination syndromes concept, proposed over 100 yr ago, attempts to predict a plant’s pollinators by its suite of floral traits, e.g. colour, size, structure of open flower (Faegri & van der Pijl 1979). The concept has been central to understanding interactions between plants and animal pollinators but has recently been criticized because the “syndromes” are rarely accurate predictors of a plant’s true pollinators (Waser et al. 1996, Hingston and McQuillan 2000, Ollerton et al. 2009, 2015). Under this concept, Corymbia’s floral traits suggest pollination by large animals: red is considered a bird-attracting floral color (Faegri & van der Pijl 1979), and the large bowlshaped open bloom (approx. 4–5 cm diameter), with style rising high above the stamens, suggests that only large animals would be able to transfer pollen successfully (Fig. 1b). Native honeyeaters and large-bodied native insects, particularly fiddler beetles (Eupoecila australasiae), flower wasps (Scolia spp.), as well as introduced European honey bees (Apis mellifera), are commonly seen foraging on open flowers during the summer bloom period. In contrast, small-bodied bees, like hylaeine bees, appear to be mostly nectar thieves on fully open Corymbia flowers, as they are able to access the nectar bowl and collect pollen from stamens without making any contact with the stigma. However, as the bud breaks open, the stamens are inflexed toward the style, gradually moving up the style and extending outwards. For a brief period during the later stages of anthesis, pollen-laden anthers are clustered in the center of the flower close to the stigma and small bees collecting pollen from the anthers would likely come in contact with it (Fig. 1a). Based on current knowledge of C. ficifolia reproduction, the behavior I observed is more likely to amount to pollen theft than pollination. Mating systems in C. ficifolia are poorly understood, although much attention has been given to development of hybrids for plantation forestry and urban street-scaping (Dickinson et al.