Re-evaluation Note REV2016-05, Re-evaluation of Imidacloprid - Preliminary Pollinator Assessment

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The online consultation is now closed.

Pest Management Regulatory Agency
18 January 2016
ISSN: 1925-0649 (PDF version)
Catalogue number: H113-5/2016-05E-PDF (PDF version)

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Table of Contents


Over the past few years, there has been an emerging body of scientific research which suggests that there may be potential short-term and long-term effects on pollinators resulting from exposure to imidacloprid. Reported effects have included changes in bee behaviour, bee mortality, and adverse effects on queens and developing bees. These studies have generally been conducted under laboratory situations or in the field with bees exposed to imidacloprid at doses higher than may normally be encountered in the environment.

In 2012, Health Canada's Pest Management Regulatory Agency (PMRA) announced the re-evaluation of neonicotinoid insecticides including imidacloprid. The re-evaluations were initiated to assess the potential risk to pollinators in light of international updates to the pollinator risk assessment framework. This re-evaluation considers all agricultural and outdoor uses of imidacloprid that could result in potential bee exposure, including foliar applications, soil applications, seed treatment applications, greenhouse and tree injection applications.

For the pollinator risk assessment, the PMRA is reviewing the emerging body of scientific research and available monitoring data to assess whether risks to pollinators from imidacloprid at the levels anticipated to be present in the Canadian environment continue to be acceptable. This includes working cooperatively with scientists from around the world.

The PMRA has requested additional data from the imidacloprid registrants which must be submitted by December 2016. In the interim, PMRA has conducted a preliminary pollinator risk assessment for foliar, soil and seed treatment applications based on currently available data. The final pollinator risk assessment will assess all imidacloprid uses and application methods.

What is Imidacloprid?

Imidacloprid is a neonicotinoid insecticide which is used to control a broad spectrum of insect pests on a wide variety of sites. This re-evaluation considers only the sites for which an environmental risk assessment for pollinators is needed, including cereals, fruits, greenhouse food and ornamental crops, herbs, legumes, oilseeds, vegetables, Christmas trees, outdoor ornamentals and turf. The Commercial Class imidacloprid products are applied using conventional ground equipment such as airblast sprayers, boom sprayers, backpack and hand wand sprayers, conventional aerial equipment (such as fixed wing and rotary aircraft), tree injection equipment, granular spreaders, chemigation equipment, seed treatment equipment (commercial treatment facilities and on-farm using closed and open systems), potato seed piece treatment equipment by farmers, farm workers and professional applicators. The Domestic Class imidacloprid products are applied by the general public using granular spreaders on turf.

What Happens When Imidacloprid is Introduced into the Environment?

Imidacloprid is a systemic insecticide which is absorbed and transported throughout the plant, thereby protecting the whole plant. Imidacloprid is readily taken up by plants through treated leaves, treated seed or roots growing in treated soil. Imidacloprid moves upward inside the plant. Pollen and nectar may contain imidacloprid as a result of this upwards movement.

Once inside the plant, imidacloprid remains the predominant residue, although many compounds are formed as a result of the plant's metabolism. Of these, 5-hydroxy-imidacloprid and imidacloprid-olefin are considered to be the most relevant for the pollinator risk assessment given their higher toxicity to bees.

Imidacloprid is persistent in the environment. In treated fields, imidacloprid has been shown to carry over from one growing season to the next. When imidacloprid is used for multiple years in succession, concentrations in soil initially increase and then stabilize after approximately three years.

Imidacloprid is water soluble and mobile in the environment. Imidacloprid can leach through the soil profile and has been detected in groundwater. Imidacloprid is routinely found in surface water, including puddles which are known drinking water sources for pollinators.

What was Considered for the Preliminary Assessment?

The review was based on the data submitted to the PMRA by the registrants and available information from the open scientific literature. The evaluation was conducted according to the Guidance for Assessing Pesticide Risks to Bees. This guidance was collaboratively developed by the PMRA, the United States Environmental Protection Agency (USEPA) and the California Department of Pesticide Regulation.

The risk assessment consists of characterizing the exposure and effects of imidacloprid to bees, and determining whether exposures resulting from its uses are expected to pose a risk of concern to bees. A tiered approach is used for characterizing the risks, from the most conservative (likely an overestimation) at the lower tier (Tier I) to more realistic at higher tiers (Tiers II and III). Effect endpoints for individual bees, colonies, and bee species other than honey bees are considered in the risk characterization.

At Tier I, individual bee effect endpoints from the laboratory are used along with conservative (likely overestimated) exposure estimates. Refinements to Tier I and higher tiers consider measured residues in pollen and nectar, and colony level effect endpoints from semi-field (tunnel studies or colony feeding studies) and field studies. In semi-field tunnel studies, bee colonies are confined in tents or tunnels with crops treated using specific application methods. In semi-field feeding studies, hives are fed with known amounts of test chemical in either sugar solution, pollen/pollen substitute, or both. In field studies, which are meant to provide the most realistic exposure scenario, unconfined colonies are placed in fields where the crops have been treated using specific application methods.

The honey bee is used in the risk assessment to represent all types of bees and other insect pollinators. Available information on other types of bees, such as bumble bees, is also considered. Information from all tiers of the risk assessment along with the associated strengths and weaknesses are considered to characterize the risk.

Crop attractiveness is considered when identifying potential risk to bees. Bees may be exposed to pesticides when they forage on crop pollen or nectar. For crops that are harvested prior to bloom, there will be no exposure to crop pollen or nectar. Some crops do not have pollen or nectar sources. Other crops may not be very attractive to bees. Therefore when crop pollen or nectar is unavailable or unattractive to bees, there is minimal potential for exposure through consumption of crop pollen and nectar, and therefore minimal risk.

Label statements also affect potential exposure to pollinators and are considered when identifying potential risk to bees. For example, foliar applications of imidacloprid include restrictions on application during-bloom, thus reducing pollinator exposure. Some crops allow only post-bloom application. As well, the Canadian labels do not allow Group 4 Insecticides (which includes imidacloprid) to be applied by multiple application methods to the same crop in the same season.

Can Approved Uses of Imidacloprid Affect Pollinators?

The risk characterizations are presented by application method to the crop (for example foliar, soil, and seed treatment). As described previously, the individual bee and colony level effects are compared to pollen and nectar residues to determine potential risk. As well, available tunnel-studies and field studies associated with specific applications are considered. In addition, current imidacloprid product label language and use directions as well as crop attractiveness to pollinators are considered in the risk characterization. This pollinator risk characterization is based on information available to date from registrants and the public literature. Additional data is expected, and will be considered when finalizing the pollinator risk assessment.

Foliar applications

Potential risk from foliar application varies with application timing. Current label restrictions aid in minimizing risk.

For foliar applications, residue information in pollen and nectar was available, although residue studies were typically conducted at rates higher than Canadian application rates and/or with crops not grown in Canada. Available residues were used to the extent possible to compare with individual and colony level effects information to characterize the risk for Canadian foliar uses.

A potential risk to bees was indicated for bee attractive crops associated with pre-bloom, during-bloom, and some post-bloom applications, however, current label restrictions minimize potential risk. A relevant Tier II tunnel study on potential risk to bees from foliar turf application suggests Canadian label mitigation adequately minimises risk for this use.

When foliar applications are used, rotational crops planted the following season are not expected to pose a risk to bees.

Foliar application during-bloom is expected to result in low risk to bees based on current label restrictions.

While foliar applications made during-bloom are expected to pose a risk to bees, current labels prohibit or reduce application during-bloom for most bee attractive crops.

Further residue information on Canadian specific agricultural crops could refine the risk assessment for pre-bloom foliar applications.

Pre-bloom foliar applications may pose a risk to bees. However, residue information for pre-bloom applications was only available on crops not grown in Canada. Pre-bloom applications are currently prohibited for some uses, including orchard crops (stone fruit and pome fruit), which are highly attractive to bees.

Post-bloom applications to orchard, tree and field agricultural crops are not expected to pose a risk to bees.

Post-bloom applications to agricultural crops that are harvested at the end of the season are not expected to pose a risk to bees, as pollen and nectar are no longer available for forage. For orchard and tree crops, there is evidence that the timing of the post-bloom application can affect the residue levels found in pollen and nectar the next season. Lower residues were observed with a longer time period between application and next season's bloom, thus affecting the potential for risk to bees. Based on available information, no potential for risk was identified when post-bloom applications were made prior to harvest.

Soil applications

A potential risk to bees was identified for some soil treatments.

The data set available to assess risk from soil applications included residue information in pollen, nectar or flowers for a variety of Canadian relevant crops and application rates. Potential for risk varied with crop, soil type, application timing relative to bloom-period and residue sampling date relative to application timing. The data set also included one relevant Tier II tunnel study to address potential for risk to bees from turf soil application. It suggests current Canadian label mitigation adequately minimises risk for use on turf. Field studies for soil treatment applications are expected in 2016 and will help further inform the pollinator risk assessment.

Higher application rates and application timing closer to plant blooming time appears to result in higher residue levels. Soil type also seems to affect residue levels. Crops grown in coarser soils (sandy soils, less organic matter) tended to have higher residues than those grown in medium or fine soils (higher organic matter).

No potential risk was identified for crops such as melon, pumpkin, and blueberry. Minimal risk is expected for bee-attractive crops in other registered crop groups (such as legumes and herbs).

Potential risk was identified for tomato and strawberry with certain application rates and soil types.

No potential risk was identified for rotational crops or off-field bee attractive forage plants which could be exposed to runoff.

Seed treatments

No potential risk to bees was indicated for seed treatment use.

The data set available to assess risk from treated seed included residue information in pollen, nectar or flowers of Canadian relevant crops, Tier II tunnel studies and Tier III field studies specific to seed treatment applications. Available higher tier tunnel-studies and field studies with seed treatments did not result in notable effects on bees.

The residue levels in crop pollen and nectar resulting from seed treatment uses are typically below levels expected to pose a risk to bees at both the individual bee and colony levels.

The exposure route of dust generated during planting of treated seed was also considered. Dust generated from planting of neonicotinoid treated corn and soybean seed was previously identified as a concern in Canada, and risk reduction measures were put in place in 2014 to reduce exposure to dust during planting of treated corn and soybean seed. Dust generation is related to multiple factors including the planting equipment and seed types, and at this time planting of other seed types in Canada is not associated with dust-generation or harm to pollinators.

What About Native Bees?

Information on native (non-Apis) bees was considered and incorporated into the pollinator risk assessment. Non-Apis bees include bees other than honey bees (Apis bees), such as bumble bees or solitary bees like the alfalfa leafcutting bee. There are approximately 1000 non-Apis bee species in Canada which have varying biological and ecological traits. Like honey bees, bumble bees live in colonies, however, their colonies are much smaller than honey bee colonies and only the queens overwinter to start a new colony every season. Unlike honey bees and bumble bees, most other non-Apis bees are solitary and nest in the ground or pithy plant stems.

Available individual bee effect information suggested that toxicity of imidacloprid to non-Apis bees is similar to that of honey bees. Tier I acute adult effect information was available for bumble bees, mason bees, leafcutting bees and stingless bees. Available Tier I effect information supports use of honey bee as a surrogate for non-Apis bees.

Available Tier II tunnel studies and Tier III field studies were consistent with tunnel and field studies on honey bees, and were used to support the overall risk conclusions for pollinators. Tier II and III studies were conducted primarily with bumble bees, and typically did not show notable effects for Canadian relevant use patterns.

Results of the available Tier II colony level feeding studies with non-Apis bees suggested that bumble bees may be more sensitive to imidacloprid exposure than honey bees. Measured pollen and nectar residues were often above the lowest dose where colony effects were detected in bumble bee feeding studies, suggesting a potential for risk. At this time, there is uncertainty as to whether colony level effects observed in feeding tests would represent impacts to bumble bee colonies in nature. Recent available non-Apis research has yet to be incorporated into the assessment; this additional information may be informative. There is also uncertainty about whether the bumble bee effects information is relevant for other non-Apis bees, such as solitary bees.

There has been additional recent research published on non-Apis bees which will be reviewed and considered for the final pollinator risk assessment. The PMRA expects that the science of non-Apis effect testing and risk assessment will continue to improve, and any new developments will also be considered in the final pollinator risk assessment.

Measures to Minimize Risk

Labels of registered pesticide products include specific instructions for use. Directions include risk-reduction measures to protect the environment, including pollinators. The current imidacloprid labels include restrictions to protect pollinators from exposure to pesticides. The need for additional mitigation measures for protection of pollinators will be developed based on the final pollinator risk assessment. Any additional data available prior to the final pollinator risk assessment will also be considered when proposing risk mitigation.

Next Steps

In order to provide the public with timely information, the PMRA published a pre-release version of REV2016-05, Re-evaluation of Imidacloprid - Preliminary Pollinator Assessment on 6 January 2016. The pre-relase document contained the Overview and Science Evaluation but it did not contain the related Appendices.

The full preliminary assessment document, containing the Appendices, is now available. The PMRA will accept written comments for up to 60 days from the date of publication of this document.

The PMRA will consider all comments received from the public in response to this consultation document. The PMRA will then publish a Proposed Re-evaluation Decision document that will include an updated final pollinator risk assessment, and related regulatory porposal.

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