A competição de abelhas noturnas, abelhas do mel e abelhas sem ferrão pelo pólen de plantas de floração maciça

Abstract

Mass flowering species, whose flowers open in large amount at the same time for a short period, are known as exceptional sources of pollen for bees. In the mass flowering species with flowers that open at night, during twilight or just before sunrise, the number of bee species that visit their flowers in search of pollen grows as the brightness increases after dawn, also increasing the competition among them. Several bee species, including crepuscular/nocturnal bees, honey bees and stingless bees exploit these flowers and compete for their pollen. However, competition for this resource was rarely quantified. We used four mass-flowering Myrtaceae species as a model, to investigate the competition among native bees and the introduced honey bees for pollen. In Campomanesia pubescens, C. adamantium, Blepharocalyx salicifolius and Myrcia rufipes, species with typical pollen flowers, we quantified how much pollen is collected by different bee groups. We conducted a pollen removal experiment in flowers accessed only by bee groups. We showed that the pollen of C. pubescens flowers was collected by crepuscular bees, honey bees and stingless bees, while in the other species the pollen was removed by honey bees and stingless bees. In all four plants species studied, honey bee workers were by far the most abundant floral visitors and the best competitors, collecting most of the flower pollen (Chapters 1, 2 and 3). In addition, we measured the impact of the massive presence of honey bees on the frequency of visits and pollen collection by native bees on C. pubescens, B. salicifolius and M. rufipes flowers (Chapters 1 and 2). In C. pubescens, the massive presence of honey bee workers shortened the effective time that crepuscular bees, the main pollinators of this species, collect pollen without competitors at dawn and strongly decrease pollen gain by diurnal native bees. However, the exclusion of honey bees from flowers resulted in a drastic increase in pollen flow for native diurnal species, especially stingless bees. In B. salicifolius and M. rufipes, after the exclusion of honey bees from the flowers, the frequency of stingless bees was threefold and the pollen gain of stingless bees increased considerably in both species. These results demonstrated that native bees are displaced by the introduced bee via exploitative competition. Despite the negative impact on native bees, the honey bees were effective pollinators of the three plant species. In chapter 4, we study aspects related to the interaction of the massive flowering species Caryocar brasiliense with bees that visit their flowers. The species has typical chiropterophilous flowers that open at night and provide resources until dawn, attracting nocturnal bees and several diurnal bee species. We evaluated the importance of C. brasiliense as a floral resource for nocturnal bees and whether, these bees act as effective pollinators of C. brasiliense flowers. Our results showed that although C. brasiliense pollen are an important food resource for nocturnal bees, these bees did not contribute to the pollination of this typical Cerrado tree.