Therefore, to ensure pollination, growers invest up to 12 honeybee colonies per ha 16, 18. While many wild bees present in blueberry native distribution are able to buzz-pollinate the anthers 18, honeybees do not have this ability and are considered less effective pollinators 19, 20. Their poricidal dehiscent anthers require buzz-pollination, i.e., the behaviour of vibrating flowers to release great amounts of pollen. Blueberry flowers are also visited for their pollen. 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 small, with urceolate corollas which limit the access of visitors to the basal nectaries. Also, blueberry cultivars exhibit diverse floral morphologies that may affect visitation rates and behaviour of pollinators 17. 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. 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. In South America acreage has expanded steadily in the last decade, with Argentina accounting for 20 thousand tons in 2018 13. Blueberry global production increased 57% between 20 12. Highbush blueberry Vaccinium corymbosum, though native to eastern North America, is now cultivated globally. Furthermore, an integrated approach combining native bees with honeybees can enhance pollination services, due to complementarity in their foraging behaviour 10, 11. Bumblebees have been proven to be efficient pollinators of greenhouse as well as of outdoor crops 8, 9. Therefore, there has been a growing interest in managing alternative species, such as bees of the genera Osmia, Bombus, and Megachile 6, 7. However, the abundance and diversity of pollinator assemblages vary in different agroecosystems, and growers often rely on managed honeybees for pollination services. 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. Similar content being viewed by othersÄespite 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. 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. 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. Both managed pollinators showed different foraging patterns, influenced by the cultivar identity which varied in their floral morphology and nectar production. 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. Thus, the South American bumblebee Bombus pauloensis is increasingly managed as an alternative species in this crop alongside honeybees. 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.
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