Pollination of Blumenbachia catharinensis (Loasaceae)—efficient pollen collection and pollen theft from the stigma by an oligolectic bee

Abstract

Many Loasaceae are characterized by specialized androecium composed of complex nectar scales and bundles of fertile stamens that present pollen through one-by-one stamen movements to the flower center over several days. It is a challenge for pollen-seeking bees to predict when the small pollen packets will be presented during the days-long staminate phase. Narrow interactions with oligolectic bee pollinators that exhibit specialized pollen foraging are characteristic for flowers of Loasoideae. We investigated the pollination system of Blumenbachia catharinensis, an endemic to the Araucaria Forest of Brazil, with a specific focus on the role of the newly described oligolectic bee Rhophitulus ater (Andrenidae). We described the pollen presentation characteristics of B. catharinensis, analyzed the foraging strategy of R. ater and its role as pollinator and determined which bee species obtains the most pollen. Females of R. ater were the dominant flower visitors (> 90% of visits) and the first to remove the pollen from > 95% of the anthers, thus gaining almost the entire pollen content of B. catharinensis flowers. During foraging flights, females always approached and hovered at a short distance in front of flowers. After ~ 80% of floral approaches, they rejected visits, particularly when no pollen-carrying anther was available. Thus, this floral inspection is a constant behavioral trait of the pollen foraging strategy of R. ater. Curiously, in more than half of the visits to pistillate-phase flowers, females actively collected the deposited allochthonous pollen present on stigma and style. Therefore, they are both pollinators and antagonistic pollen thieves for B. catharinensis.