While morphological differences such as tongue length are often featured as drivers of pollinator floral preferences, differences in chemical detection and tolerance to secondary compounds may also play a role. We sought to better understand the role of secondary compounds in floral preference by examining visitation of milkweed flowers, which can contain toxic cardenolides in their nectar, by bumble bees (Bombus spp.), some of their most abundant and important pollinators. We examine bumble bee species visitation of common milkweed (Asclepias syriaca) compared to other flowers in the field and test whether observed preferences may be influenced by avoidance and tolerance of cardenolides, as measured by the cardenolide ouabain, in the lab. We reveal that common milkweed is visited predominantly by one bumble bee species, Bombus griseocollis, in a ratio much higher than the abundance of this species in the community. We confirmed the presence and toxicity of cardenolides in A. syriaca nectar. Lab experiments revealed that B. griseocollis, compared to the common bumble bees B. impatiens and B. bimaculatus, exhibit greater avoidance of cardenolides, but only at levels that start to induce illness, whereas the other species exhibit either no or reduced avoidance of cardenolides, resulting in illness and mortality in these bees. Toxicity experiments reveal that B. griseocollis also has a substantially higher tolerance for cardenolides than B. impatiens. Together, these results support a potential evolutionary association between B. griseocollis and milkweed that may involve increased ability to both detect and tolerate milkweed cardenolides.

虽然形态差异（例如舌头长度）通常是授粉媒介花卉偏好的驱动因素，但化学检测和对次要化合物的耐受性差异也可能起作用。我们试图更好地了解花卉偏好次生化合物通过检查的马利筋的花，它可以包含有毒的卡烯内酯在他们的花蜜，通过熊蜂探视的作用（熊蜂属），他们的一些最丰富和重要的授粉。我们研究了常见的马利筋（Asclepias syriaca）的大黄蜂物种访问）与该领域的其他花朵进行比较，并在实验室中测试观察到的喜好是否可能受到对烯醇内酯的规避和耐受性的影响（如对烯醇内酯哇巴因的测量）。我们发现普通乳草主要由一种大黄蜂（Bombus griseocollis）访问，其比例远高于该物种在社区中的丰富度。我们证实了芥菜蜜中烯醇内酯的存在和毒性。实验室实验表明，与常见的大黄蜂B. impatiens和B. bimaculatus相比，B。griseocollis，表现出更大的避免烯醇内酯的能力，但仅在开始引起疾病的水平上，而其他物种则没有或没有避免烯醇内酯的存在，从而导致这些蜜蜂的疾病和死亡。毒性实验表明，灰藓芽孢杆菌比凤仙芽孢杆菌对烯醇内酯的耐受性也高得多。总之，这些结果支持灰黄芽孢杆菌和马利筋之间的潜在进化关联，这可能涉及增加的检测和耐受马利筋烯醇内酯的能力。