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Keywords: Asian honey bees; Gnetum; gymnosperms; moths; nocturnal pollination; plant-insect interactions; pollen theft; tropical rainforests EN Asian honey bees Gnetum gymnosperms moths nocturnal pollination plant-insect interactions pollen theft tropical rainforests 1 4 4 12/03/21 20211201 NES 211201 Bees belong to modern groups of pollinators, which originated concurrently with new angiosperms (flowering plants), and might have contributed to the global gymnosperm-to-angiosperm turnover in the mid-Cretaceous (125-90 million years ago [Ma]; Cardinal and Danforth 2013, Peris et al. 2017). Our data suggest that diurnal honey bees disrupt the pollination of an insect-pollinated gymnosperm by reducing the pool of pollen available for nocturnal pollinators, resulting in decreased pollinator pollen loads and reduced seed set. Then, in bee-present season, we quantified honey bee visitation rate, pollen loads on honey bees and pollen remaining in anthers after honey bee visits to assess the intensity of theft. [Extracted from the article]

Pollen is unique among floral rewards in functioning as both a carrier of gametes and an attractant and nutritious resource for floral visitors. Animals that collect pollen without pollinating (pollen thieves) could reduce siring success of thieved plants and cause pollen limitation of seed set at the population level; however, such impacts on plant reproduction have not been demonstrated experimentally. To test these effects we added hives of native honey bees (Apis mellifera scutellata) to populations of a primarily bird-pollinated plant, Aloe maculata, in eastern South Africa. In field and aviary trials, bee addition increased pollen removal from anthers but decreased pollen deposition on stigmas, and so reduced both male and female pollination components. Further, total seed production decreased with hive addition in the aviary experiment and in three of four field populations, indicating that population-level pollen theft can also compromise reproductive success. In the field, naturally occurring allodapine bees also seemed to act as pollen thieves, outweighing the effect of honey bee hive addition at one of the four aloe populations. Our results highlight the importance of social bees as pollen thieves, even of plants that have evolved in their presence, and the role of dichogamy in promoting pollen theft. Given the commonness of both social bees and dichogamy, pollen theft is likely a much more common influence on floral ecology and evolution than suggested by the sparse literature. [ABSTRACT FROM AUTHOR]