Influence of Pollen Nutrition on Honey Bee Health: Do Pollen Quality and Diversity Matter?

Honey bee colonies are highly dependent upon the availability of floral resources from which they get the nutrients (notably pollen) necessary to their development and survival. However, foraging areas are currently affected by the intensification of agriculture and landscape alteration. Bees are therefore confronted to disparities in time and space of floral resource abundance, type and diversity, which might provide inadequate nutrition and endanger colonies. The beneficial influence of pollen availability on bee health is well-established but whether quality and diversity of pollen diets can modify bee health remains largely unknown. We therefore tested the influence of pollen diet quality (different monofloral pollens) and diversity (polyfloral pollen diet) on the physiology of young nurse bees, which have a distinct nutritional physiology (e.g. hypopharyngeal gland development and vitellogenin level), and on the tolerance to the microsporidian parasite Nosemaceranae by measuring bee survival and the activity of different enzymes potentially involved in bee health and defense response (glutathione-S-transferase (detoxification), phenoloxidase (immunity) and alkaline phosphatase (metabolism)). We found that both nurse bee physiology and the tolerance to the parasite were affected by pollen quality. Pollen diet diversity had no effect on the nurse bee physiology and the survival of healthy bees. However, when parasitized, bees fed with the polyfloral blend lived longer than bees fed with monofloral pollens, excepted for the protein-richest monofloral pollen. Furthermore, the survival was positively correlated to alkaline phosphatase activity in healthy bees and to phenoloxydase activities in infected bees. Our results support the idea that both the quality and diversity (in a specific context) of pollen can shape bee physiology and might help to better understand the influence of agriculture and land-use intensification on bee nutrition and health.

蜜蜂蜂群高度依赖花源资源的可获取性，其生长发育与生存所需的营养物质（尤其是花粉）均取自此类资源。然而当前蜜蜂的觅食区域正受到农业集约化与景观改造的影响。因此，蜜蜂面临花源资源丰度、类型与多样性的时空分布不均问题，这可能导致营养供给不足，进而威胁蜂群存活。花粉可获得性对蜜蜂健康的有益影响已得到广泛证实，但花粉日粮的品质与多样性能否改善蜜蜂健康，目前仍知之甚少。为此，我们测试了花粉日粮品质（不同单花花粉）与多样性（多花花粉日粮）对幼龄保育蜂生理状态的影响——这类保育蜂具有独特的营养生理特征，例如咽下腺发育与卵黄原蛋白水平——以及对微孢子虫寄生虫（Nosema ceranae）的耐受能力；测试通过测定蜜蜂存活率，以及与蜜蜂健康和防御反应相关的多种酶活性来完成，相关酶包括谷胱甘肽S-转移酶（glutathione-S-transferase，参与解毒作用）、酚氧化酶（phenoloxidase，参与免疫功能）与碱性磷酸酶（alkaline phosphatase，参与代谢过程）。研究结果显示，保育蜂的生理状态与对该寄生虫的耐受能力均受花粉品质的影响。花粉日粮多样性对保育蜂生理状态与健康蜜蜂的存活率均无显著影响。然而，当被寄生虫感染后，饲喂多花花粉混合日粮的蜜蜂寿命长于饲喂单花花粉的蜜蜂，蛋白质含量最丰富的单花花粉组除外。此外，健康蜜蜂的存活率与碱性磷酸酶活性呈正相关，而感染寄生虫的蜜蜂存活率则与酚氧化酶活性呈正相关。本研究结果支持以下观点：花粉的品质与（特定情境下的）多样性均可塑造蜜蜂的生理状态，这有助于我们更深入理解农业集约化与土地利用方式改变对蜜蜂营养状况与健康的影响。