Managed honeybees and South American bumblebees exhibit complementary foraging patterns in highbush blueberry (original) (raw)

Despite Apis mellifera being the most widely managed pollinator to enhance crop production, they are not the most suitable species for highbush blueberries, which possess restrictive floral morphology and require buzz-pollination. Thus, the South American bumblebee Bombus pauloensis is increasingly managed as an alternative species in this crop alongside honeybees. Herein, we evaluated the foraging patterns of the two species, concerning the potential pollen transfer between two blueberry co-blooming cultivars grown under open high tunnels during two seasons considering different colony densities. Both managed pollinators showed different foraging patterns, influenced by the cultivar identity which varied in their floral morphology and nectar production. Our results demonstrate that both species are efficient foragers on highbush blueberry and further suggest that they contribute positively to its pollination in complementary ways: while bumblebees were more effective at the individual level (visited more flowers and carried more pollen), the greater densities of honeybee foragers overcame the difficulties imposed by the flower morphology, irrespective of the stocking rate. This study supports the addition of managed native bumblebees alongside honeybees to enhance pollination services and emphasizes the importance of examining behavioural aspects to optimize management practices in pollinator-dependent crops. Despite honeybees being the most adaptable and widely managed pollinator to enhance crop production 1 , the global stock of Apis mellifera colonies is growing slower than agricultural demands for pollination services 2. With the expansion of areas cultivated with pollinator-dependent crops around the globe 3 , the contribution of wild insects to pollination has been recognized for a wide variety of annual and perennial species 4,5. However, the abundance and diversity of pollinator assemblages vary in different agroecosystems, and growers often rely on managed honeybees for pollination services. Therefore, there has been a growing interest in managing alternative species, such as bees of the genera Osmia, Bombus, and Megachile 6,7. Bumblebees have been proven to be efficient pollinators of greenhouse as well as of outdoor crops 8,9. Furthermore, an integrated approach combining native bees with honeybees can enhance pollination services, due to complementarity in their foraging behaviour 10,11. Highbush blueberry Vaccinium corymbosum, though native to eastern North America, is now cultivated globally. Blueberry global production increased 57% between 2013 and 2018 12. In South America acreage has expanded steadily in the last decade, with Argentina accounting for 20 thousand tons in 2018 13. In these latitudes, southern cultivars are being grown, which were originally developed in the 1980s in Florida where highbush blueberries could not meet their high chilling requirement 14. The numerous cultivars resulting from selective breeding, present varying degrees of pollinator dependency, yet all benefit from cross-pollination and hence two or more cultivars are usually planted in adjacent rows 15,16. Also, blueberry cultivars exhibit diverse floral morphologies that may affect visitation rates and behaviour of pollinators 17. Blueberry flowers are small, with urceolate corollas which limit the access of visitors to the basal nectaries. In addition to its accessibility, intraspecific variability of the quantity and quality of nectar could modify the attractiveness of different cultivars to bees. Blueberry flowers are also visited for their pollen. Their poricidal dehiscent anthers require buzz-pollination,