The challenge of balancing fungicide use and pollinator health

Human crop production has benefitted from developments in the use of natural and formulated chemical substances to control pathogens and insect herbivores. However, numerous adverse effects of exposure to these chemical substances, pesticides, have been documented in a variety of nontarget organisms. Of particular concern are the negative impacts of pesticide exposure on agriculturally important insect pollinators. While the general effects of pesticides on pollinator health have garnered much interest, the potential role of certain pesticide classes has historically been poorly understood and investigated. Despite their ubiquity in the foraging environment, fungicides were traditionally deemed to be safe for pollinating insects based on low toxicity outcomes in standardized assessments by regulatory agencies. Recently, multiple studies have dispelled this traditional designation by demonstrating numerous sublethal and lethal outcomes for pollinators exposed to various fungicides. Here we provide an overview of the historical underpinnings of fungicide development and application, as well as trends in the implementation of regulatory measures. We discuss exposure routes and the prevalence of fungicides in the environment. Finally, we explore the growing body of literature revealing negative effects of exposure including the specific mechanisms by which fungicides act on non-target pollinators, including fungicide synergisms with other pesticide classes, pests, pathogens and phytochemicals, and fungicide-induced behavioural alterations.