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

Abstract

Background Pollinating insects provide economically and ecologically valuable services, but are threatened by a variety of anthropogenic changes. The availability and quality of floral resources may be affected by anthropogenic land use. For example, flower-visiting insects in agroecosystems rely on weeds on field edges for foraging resources, but these weeds are often exposed to agrochemicals that may compromise the quality of their floral resources. Methods We conducted complementary field and greenhouse experiments to evaluate the: (1) effect of low concentrations of agrochemical exposure on nectar and pollen quality and (2) relationship between floral resource quality and insect visitation. We applied the same agrochemcial treatments (low concentrations of fertilizer, low concentrations of herbicide, a combination of both, and a control of just water) to seven plant species in the field and greenhouse. We collected data on floral visitation by insects in the field experiment for two field seasons and collected pollen and nectar from focal plants in the greenhouse to avoid interfering with insect visitation in the field. Results 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.

Effect of herbicides on pollinator foraging behavior and flower morphology in white clover (Trifolium repens L.)–infested turfgrass

“…The authors speculated that dicamba may have reduced nectar production in exposed plants (Bohnenblust et al 2016). Drift of glyphosate to field-edge plants reduced nectar production 14 DAT (Russo et al 2022).…”

The nutritional landscape in agroecosystems: a review on how resources and management practices can shape pollinator health in agricultural environments

“…Such negative impacts on the soil can affect floral traits that influence pollinator attraction and have implications on both pollinator health and crop yield (David et al 2019, Dai et al 2022, Filipiak et al 2022b, Vaudo et al 2022). Skewed nutrient ratios in the soil can affect the total number of flowers and resource nutritional quality and quantity (Vaudo et al 2022, Russo et al 2023). In contrast, no-till management practices can minimize the effects of soil erosion and nutrient loss (Pesant et al 1987), and reduced tillage can increase soil moisture by reducing evaporation rates, decreasing surface water runoff, and improving water infiltration into the soil (McVay et al 2006, Tyler and Locke 2018).…”