Abstract
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.
Highlights
The western honey bee (Apis mellifera) is a eusocial species whose foragers collect food to meet hive requirements and adjust their food-gathering behavior according to these collective needs
A flavonol found in many honeys, essentially all pollen, and in propolis in many parts of the world, upregulates at least 12 genes encoding cytochrome P450 monooxygenases, including CYP9Q1, CYP9Q2, and CYP9Q3, which detoxify both tau-fluvalinate and coumaphos[14] and enhances longevity of workers exposed to the pyrethroid insecticide β-cyfluthrin[15]
With respect to phenolic acids, evidence of discriminative behaviour was found only for sugar water containing caffeic acid; foragers showed an avoidance response according to the visitation frequency ratio at 1 ppm (one-sample t(4) = −2.908, p = 0.044) but showed a preference according to the consumption ratio at the same concentration (one-sample t(4) = 23.522, p < 0.001)
Summary
The western honey bee (Apis mellifera) is a eusocial species whose foragers collect food to meet hive requirements and adjust their food-gathering behavior according to these collective needs. This assay was used to compare honey bee foraging responses to natural phytochemicals and synthetic xenobiotics found as common contaminants in U.S beehives.
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