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Shortfalls of EPA’s Preliminary Risk Assessment for Imidacloprid

By Scott Hoffman Black, Rich Hatfield, Thelma Heidel-Baker, and Sarina Jepsen on 7. January 2016
Scott Hoffman Black, Rich Hatfield, Thelma Heidel-Baker, and Sarina Jepsen

The US Environmental Protection Agency (EPA) has announced a preliminary pollinator risk assessment for the neonicotinoid insecticide, imidacloprid, which shows a threat to some pollinators. The EPA’s assessment indicates that the highly toxic, long-lived neonicotinoid imidacloprid “potentially poses risk to hives when the pesticide comes in contact with certain crops that attract pollinators…”

While we are pleased that the EPA released this initial assessment, our review of the documents shows severe shortfalls in the methods and omissions in the evaluation which will allow continued risk to both native pollinators and to honey bees.


honey bee on sunflower
The EPA’s Preliminary Risk Assessment for insecticides potentially harmful to bees focused on the risk to honey bees, ignoring the risks to some 3,600 species of bees native to the United States. (Photo: Public Domain)


Some of the most concerning issues Xerces noted in the preliminary assessment are that:

The EPA used managed honey bees as surrogates for native bees even while it acknowledges that native bees face potentially greater risks. By focusing on impacts to honey bees, the EPA’s assessment ignores the many peer-reviewed studies that show impact to native bees and butterflies from imidacloprid. Pollination by native bees is estimated to be worth over $3 billion a year to the US economy. A final risk assessment must assess risk to a full suite of pollinators.

The EPA failed to address the risks caused when imidacloprid is mixed with other chemicals, even though bees often experience multiple chemical exposures. For example, while the EPA recognizes that fungicides mixed with neonicotinoids can cause greater than additive effects, it still stated that “…the extent of this relationship is beyond the scope of this assessment.”  A final risk assessment needs to look at exposure from multiple chemicals.

The EPA disregards the clear risk to bumble bees and other native bees from the use of imidacloprid on tomato production. While harmful residue levels of imidacloprid are expected from tomato production, the EPA determined there was low risk because honey bees are not attracted to tomatoes. In contrast, bumble bees and other non-Apis pollinators are regular visitors to and essential pollinators of tomatoes, greatly improving fruit yield. The EPA’s justification fails to acknowledge the importance of non-Apis pollinators to tomato crop systems, potentially putting several species of important crop pollinators at risk. With more than one quarter of North American bumble bees at risk of extinction, the EPA must be more responsive to the risks to native bumble bees in the final risk assessment.

The EPA failed to evaluate potential risks of imidacloprid to declining monarch butterflies. With on-going work from multiple federal agencies to restore monarch habitat, including the EPA’s own effort to determine mitigation measures to reduce pesticide impacts on monarchs, the decision to exclude monarchs from this pollinator risk assessment is a lost opportunity. The final risk assessment should evaluate the potential risk to monarchs from imidacloprid use.

Even with these limitations, the EPA’s preliminary assessment recognizes significant risks from the legal use of imidacloprid. If these risks are to be reversed, the EPA must suspend the use of imidacloprid until we know if and how it can be used without threatening bees and other pollinators.

It must be recognized that this assessment addresses the impacts of only one neonicotinoid on one group of beneficial insects. Preliminary pollinator risk assessments for three other neonicotinoids, clothianidin, thiamethoxam, and dinotefuran, are scheduled to be released for public comment in December 2016. At that same time, the EPA plans to release a risk assessment on the effects of imidacloprid to birds, aquatic species, and other animals. Despite the fact that neonicotinoids are now widely found in both terrestrial and aquatic habitats, the EPA’s piecemeal process does not include an overarching review of the broader interactions and ecosystem effects from the use of these products.

The Xerces Society hopes that the final pollinator risk assessment for imidacloprid will address the deficiencies noted above and that these issues will be adequately addressed in the pollinator risk assessments for the other three pesticides.



Rich manages all aspects of the Xerces Society’s work on bumble bees. Rich has a master’s degree in conservation biology from San Francisco State University, and he joined the Xerces Society in 2012. While earning his degree, his thesis focused on local- and landscape-level factors that contribute to bumble bee species richness and abundance. He has also investigated native bee pollination in agricultural systems in the Central Valley of California and researched endangered butterflies in the San Juan Mountains of Colorado, as well as throughout the Pacific Northwest.

Sarina directs the Xerces Society’s Endangered Species and Aquatic Program. Since joining the Society in 2006, Sarina has worked on the conservation of diverse at-risk North American invertebrate species, including bees, butterflies, beetles, and freshwater mussels. Sarina has authored multiple publications on the conservation of endangered pollinators and other at-risk species, and developed management guidance for federal agencies, such as the U.S. Forest Service, Bureau of Land Management, and Fish and Wildlife Service.
Scott Black is an internationally renowned conservationist who has been at the forefront of the conservation movement for three decades. Scott’s work has led to protection and restoration of habitat on millions of acres of rangelands, forests, and farmland as well as protection for many endangered species. He is an author of the best-selling Attracting Native Pollinators and Gardening for Butterflies and has written more than two hundred other publications including a recent chapter on climate change and insects. Scott serves on the science advisory committee of Nature-Based Climate Solutions, which brings together stakeholders to accelerate the implementation of carbon removal strategies that simultaneously improve the social, economic, and environmental resilience of local communities.

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