Fertilizer and herbicide alter nectar and pollen quality with consequences for pollinator floral choices

<p><span>Flower-visiting insects in agroecosystems forage on weeds exposed to agrochemicals that may compromise the quality of their floral resources. We conducted complementary field and greenhouse experiments to evaluate: 1) the effect of low concentrations of agrochemical exposure on nectar and pollen quality and 2) the relationship between floral resource quality and insect visitation. We found pollen amino acid concentrations were lower in plants exposed to low concentrations of herbicide, and pollen fatty acid concentrations were lower in plants exposed to low concentrations of fertilizer, while nectar amino acids were higher in plants exposed to low concentrations of either fertilizer or herbicide. Exposure to low fertilizer concentrations also increased the quantity of pollen and nectar produced per flower. The responses of plants exposed to the experimental treatments in the greenhouse helped explain insect visitation in the field study. The insect visitation rate correlated with nectar amino acids, pollen amino acids, and pollen fatty acids. An interaction between pollen protein and floral display suggested pollen amino acid concentrations drove insect preference among plant species when floral display sizes were large. We show that floral resource quality is sensitive to agrochemical exposure and that flower-visiting insects are sensitive to variation in floral resource quality.</span></p>