Competition between the oligolectic beePtilothrix plumata (Anthophoridae) and the flower closing beetlePristimerus calcaratus (Curculionidae) for floral resources ofPavonia cancellata (Malvaceae)

The flowers ofPavonia cancellata, a creeping ruderal half-shrub of northeastern Brazil, open synchronously at 6:00 h with all anthers already dehisced. The oligolectic beePtilothrix plumata was the most effective pollinator. During 90—180 min, female bees make up to 40 brief pollen collection trips to provision their brood cells. The pollen of about 40 flowers ofP. cancellata is needed to feed one bee larva. The most frequent flower visitors, however, are the specialized curculionid beetlesPristimerus calcaratus, which do not crosspollinate 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 already been closed by the beetles. We interpret the fast, uninterrupted pollen foraging ofPtilothrix plumata bees as a strategy adapted to synchronous pollen presentation ofPavonia and to competition withPristimerus calcaratus: the female bees have to provision their brood cells before the beetles succeed in closing the flowers.