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Notes from the Lab

A roadmap for how to minimize pesticide risk to bees

- July 1, 2019 - Scott McArt - (excerpt)

Dr. Doug Sponsler

Every three years, many of the main players who are working to understand and improve pollinator health get together at the International Conference on Pollinator Biology Health and Policy (also called the “International Pollinator Conference”). This year’s conference is from July 17-20 at the UC Davis Honey and Pollination Center ( and the theme is “Multidimensional Solutions to Current and Future Threats to Pollinator Health.”

If anything is clear regarding pollinator health, it’s that no silver bullet exists to cure the current problem. Indeed, multidimensional solutions are necessary, not just advisable. Thus, on the eve of the 2019 International Pollinator Conference, it’s timely that several leading researchers in the field of pesticide-pollinator interactions published a synthesis on the topic. The paper, Pesticides and pollinators: A sociological synthesis,” written by Doug Sponsler and colleagues and published in the journal Science of the Total Environment [662:1012-1027 (2019)], gives a roadmap for how biologists, social scientists, regulatory agencies and stakeholders must work together to minimize risk to bees. In other words, their paper outlines a multidimensional solution on the topic of pesticide risk to bees.

Sponsler and colleagues’ synthesis was motivated by three key observations. First, despite a recent uptick in research on pesticide-pollinator interactions, scientists have a relatively poor understanding of the patterns and processes that govern exposure of pollinators to pesticides. Specifically, when growers, homeowners, or other pesticide applicators use a pesticide, we often don’t know whether that pesticide will end up being encountered by bees, and in what quantity.

Second, while there’s a wealth of knowledge on the toxicity of most pesticides to individual bees (especially the honey bee, Apis mellifera), we know relatively little about how toxicity to individual bees is linked to colony- or population-level outcomes. In other words, estimates of pesticide risk to bees are often occurring at the individual bee level, not at the colony level for social bees, or the population level for solitary and social bees.

Finally, links between pesticide risk (typically determined by scientists), pollination services and apicultural productivity (typically determined by growers and beekeepers) and biodiversity conservation (explicit goals of government regulatory agencies) are rarely made. It’s these missing linkages that need to occur more often if pesticide risk to pollinators is to improve.

So, where should we be focusing efforts to make the links stronger? To start getting at this important question, Sponsler and colleagues created a conceptual framework for the pollinator-pesticide system based on three interlocking domains (Fig. 1). Domain 1 focuses on the human and ecological drivers governing pesticide use. In other words, what are the motivations for using pesticides? While pest pressure (or perceived pest pressure) is of course important, the decision of when and how to use a pesticide is largely governed by socioeconomic factors, such as pesticide availability and cost, values of the applicator, and availability of information. Thus, right off the bat it’s clear that economics and human behavior drive the potential for bees to be exposed to pesticides.

The outcome of Domain 1 (i.e., how pesticides are used in space and time) comprise the inputs to Domain 2, where a pesticide’s fate in the environment interacts with pollinator behavior and life-history to determine exposure. In this Domain we figure out when and where a pollinator will come into contact with a pesticide, and at what quantity. This is the realm of biology, specifically the field of ecotoxicology.

Next, in Domain 3, patterns of exposure interact with pesticide toxicity to determine effects at the individual, colony, population, and ecosystem levels. It is here that pesticide risk is assessed (which is simply the combination of exposure and effects). Again, this is the realm of biology, often measured via laboratory “effects” assays, and occasionally via ambitious field and semi-field experiments. The idea is to challenge a pollinator with a particular dose of a pesticide, as determined via exposure data, and see whether that dose impacts the organism, colony, population or services provided by the pollinator (e.g., pollination).

Finally (and most importantly), there’s a ….