Competition between the oligolectic bee Ptilothrix plumata (Anthophoridae)and the flower closing beetle Pristimerus calcaratus (Curculionidae) for floral resources of Pavonia cancellata (Malvaceae)

The flowers of Pavonia cancellata, a creeping ruderal half-shrub of northea stern Brazil, open synchronously at 6:00 h with all anthers already dehisce d. The oligolectic bee Ptilothrix plumata was the most effective pollinator . During 90-180 min, female bees make up to 40 brief pollen collection trip s to provision their brood cells. The pollen of abo ut 40 flowers of P. can cellata is needed to feed one bee larva. The most frequent flower visitors, however, are the specialized curculionid beetles Pristimerus calcaratus, w hich do not cross-pollinate the flowers. They perforate the epidermis with their mouthparts, provoking dehydration, and then actively close the loose petals with their legs. Two hours after opening, half of the flowers had al ready been closed by the beetles. We interpret the fast, uninterrupted poll en foraging of Ptilothrix plumata bees as a strategy adapted to synchronous pollen presentation of Pavonia and to competition with Pristimerus calcara tus: the female bees have to provision their brood cells before the beetles succeed in closing the flowers.