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

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..., Greenhouse Study Design
We selected seven plant species for our experiment (Cirsium vulgare, (Savi) Ten. Asteraceae, Epilobium hirsutum, L. Onagraceae, Filipendula ulmaria, (L.) Maxim. Rosaceae, Hypochaeris radicata, L. Asteraceae, Origanum vulgare, L. Lamiaceae, Phacelia tanacetifolia, Benth. Boraginaceae, and Plantago lanceolata, L. Plantaginaceae). These comprised six native perennial and one non-native annual herbaceous species (P. tanacetifolia), selected as pollinator-attractive (Clifford, 1962; Russo et al., 2022), and likely to be found on agricultural field edges in Europe. They represent a diverse group of plant families with regard to floral resource quality (Ruedenauer et al., 2019b; Vaudo et al., 2020; Zu et al., 2021).
To collect sufficient quantities of pollen and nectar for nutritional analyses from each species in each treatment, and to avoid interrupting natural patterns of insect visitation in the field, we conducted a concurrent greenhouse study. We collected 20 wild...,