Beekeepers have long sought food and non-food supplements to "improve" the health and productivity of their bees. Often these are applied with little or no understanding of the why or how of what they actually do. 

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While the natural foods of the western honey bee (Apis mellifera) contain diverse phytochemicals, in contemporary agroecosystems honey bees also encounter pesticides as floral tissue contaminants. Whereas some ubiquitous phytochemicals in bee foods up-regulate detoxification and immunity genes, thereby benefiting nestmates, many agrochemical pesticides adversely affect bee health even at sublethal levels. How honey bees assess xenobiotic risk to nestmates as they forage is poorly understood. 

Accordingly, we tested nine phytochemicals ubiquitous in nectar, pollen, or propolis, as well as five synthetic xenobiotics that frequently contaminate hives—two herbicides (atrazine and glyphosate) and three fungicides (boscalid, chlorothalonil, and prochloraz). In semi-field free-flight experiments, bees were offered a choice between paired sugar water feeders amended with either a xenobiotic or solvent only (control). Among the phytochemicals, foragers consistently preferred quercetin at all five concentrations tested, as evidenced by both visitation frequency and consumption rates. 

This preference may reflect the long evolutionary association between honey bees and floral tissues. Of pesticides eliciting a response, bees displayed a preference at specific concentrations for glyphosate and chlorothalonil. This paradoxical preference may account for the frequency with which these pesticides occur as hive contaminants and suggests that they present a greater risk factor for honey bee health than previously suspected.

Quercetin, a flavonol found in many honeys, essentially all pollen, and in propolis in many parts of the world, also upregulates at least 12 genes encoding cytochrome P450 monooxygenases, including CYP9Q1, CYP9Q2, and CYP9Q3, which detoxify both tau-fluvalinate and coumaphos14 and enhances longevity of workers ... In contrast with at least some phytochemicals, exposure to pesticides rarely if ever is beneficial to bees; rather, pesticide ingestion is associated with a wide array of negative effects

Among all tested natural xenobiotics, foragers consistently showed a preference for quercetin according to both visitation frequency ratios and preference ratios at all concentrations. This clear predilection for quercetin under the conditions of the free-flight assay is indicative of its biological significance to honey bees.

Liao, L. H., Wu, W. Y., & Berenbaum, M. R. (2017). Behavioral responses of honey bees (Apis mellifera) to natural and synthetic xenobiotics in food. Scientific reports, 7(1), 15924.

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