Abstract

Caffeine and ethanol are naturally occurring compounds in floral nectar. We examined how these compounds influenced pollinator behaviors including floral preference, floral constancy, and social behavior using bumblebees, Bombus impatiens, which were given prior experience foraging on either human blue or human white (hereafter blue and white) artificial flowers. Because flower color influenced bee behavior, with strong preferences for blue, we focused on the interaction between nectar chemistry and flower color. Bees that had experience with blue flowers preferred blue regardless of nectar chemistry. In contrast, for bees that had prior experience with white flowers, only the control treatment preferred white, while bees exposed to caffeine and ethanol showed no preference. The effects of nectar compounds may therefore only occur when bees are already foraging on a less-preferred color. We also examined the impact of nectar chemistry on the social behavior of joining other bees at flowers. In the same treatments for which bees showed a preference for previously experienced flower colors (all of the blue treatments and only the white control), bees also preferentially visited unoccupied flowers. In the treatments where bees showed no color preference, however (the white caffeine and ethanol treatments), bees showed no preference for unoccupied flowers. We show that the impacts of field-realistic levels of caffeine and ethanol in nectar on pollinator behavior depend on flower color, highlighting that the potential costs and benefits of nectar chemistry to plants are likely to be dependent on bee behavioral biases for other floral traits.

Significance statement

Flower nectar often contains toxic compounds hypothesized to impact pollination, but little research has shown their effects on the behavioral decisions of free-flying bees. Caffeine and alcohol occur in the nectar of some flowers. We found that bee response to these nectar compounds depends on the flower color. Bees preferentially visited blue flowers regardless of nectar chemistry, but the presence of caffeine or alcohol reduced bee color preference when bees had experience foraging on white flowers. The bumblebee’s social behavior of joining other bees at flowers showed related effects; in treatments where bees showed a preference for flower type, they also preferred to forage alone. This research highlights that bees make decisions based on the interaction between multimodal cues including nectar chemistry, and therefore the strength of selection on nectar chemistry is dependent on bee behavioral biases for other floral traits.

中文翻译：

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花蜜中的咖啡因和乙醇与影响大黄蜂行为的花色相互作用

摘要

咖啡因和乙醇是花蜜中天然存在的化合物。我们研究了这些化合物如何影响传粉者的行为，包括花的偏好、花的恒常性和使用大黄蜂、凤仙花的社会行为，它们有过在人蓝色或人白色（以下称为蓝色和白色）人造花上觅食的经验。因为花色影响蜜蜂的行为，对蓝色有强烈的偏好，我们专注于花蜜化学和花色之间的相互作用。无论花蜜化学成分如何，有过蓝色花朵经验的蜜蜂都喜欢蓝色。相比之下，对于有过白花经验的蜜蜂，只有对照处理更喜欢白色，而接触咖啡因和乙醇的蜜蜂则没有表现出偏好。因此，花蜜化合物的影响可能只发生在蜜蜂已经在觅食不太喜欢的颜色时。我们还研究了花蜜化学对在花丛中加入其他蜜蜂的社会行为的影响。在蜜蜂表现出对先前经历过的花朵颜色的偏好的相同处理中（所有蓝色处理，只有白色对照），蜜蜂也优先访问未被占用的花朵。然而，在蜜蜂没有表现出颜色偏好的处理中（白咖啡因和乙醇处理），蜜蜂对空花没有表现出偏好。我们表明，花蜜中咖啡因和乙醇的实际田间水平对传粉者行为的影响取决于花的颜色，强调花蜜化学对植物的潜在成本和收益可能取决于蜜蜂对其他花性状的行为偏见。然而（白咖啡因和乙醇处理），蜜蜂对空置的花朵没有偏好。我们表明，花蜜中咖啡因和乙醇的实际田间水平对传粉者行为的影响取决于花的颜色，强调花蜜化学对植物的潜在成本和收益可能取决于蜜蜂对其他花性状的行为偏见。然而（白咖啡因和乙醇处理），蜜蜂对空置的花朵没有偏好。我们表明，花蜜中咖啡因和乙醇的实际田间水平对传粉者行为的影响取决于花的颜色，强调花蜜化学对植物的潜在成本和收益可能取决于蜜蜂对其他花性状的行为偏见。

意义陈述

花蜜通常含有被认为会影响授粉的有毒化合物，但很少有研究表明它们对自由飞翔的蜜蜂的行为决定有影响。一些花的花蜜中含有咖啡因和酒精。我们发现蜜蜂对这些花蜜化合物的反应取决于花的颜色。无论花蜜的化学成分如何，蜜蜂都会优先访问蓝色花朵，但当蜜蜂在白色花朵上觅食时，咖啡因或酒精的存在会降低蜜蜂的颜色偏好。大黄蜂在花丛中加入其他蜜蜂的社会行为显示出相关影响；在蜜蜂表现出偏爱花型的处理中，它们也更喜欢单独觅食。这项研究强调蜜蜂根据多模式线索之间的相互作用做出决策，包括花蜜化学，