Bee Precaution Pesticide Ratings

  • Frequently Asked Questions (FAQs)

Questions About the Ratings

  1. What is the purpose of the Bee Precaution Pesticide Ratings?

    To help users make an informed decision about how to reduce bee poisoning when choosing and applying pesticides.

  2. Do the ratings in this tool differ from the pollinator precautionary statement on a pesticide label?

    Yes, statements on pesticide labels may differ from the ratings provided here. The "Environmental Hazards," "Precautionary Statements," or "Protection of Pollinators" sections of some pesticide labels include a bee hazard warning, or pollinator precautionary statement and sometimes a "Bee Hazard" graphic. Legally, pesticide users must follow the product directions and take at least the minimum precautions required by the pesticide label and regulations. When not prohibited by (not in conflict with) the label or regulations, users are allowed to take more protective (restrictive) actions, such as those in the Bee Precaution Pesticide Ratings.

  3. What is the source of information and data that were used to establish pesticide ratings in the Bee Precaution Pesticide Ratings?

    The Bee Precaution Pesticide Ratings are based on the authors' consideration of

    • registration reports from government agencies that regulate (register) pesticides
    • open (public) literature, such as that on bee effects published in scientific journals
    • their professional expertise, in collaboration with coauthors and contributors to this tool

    The U.S. Environmental Protection Agency (EPA, or U.S. EPA) and pesticide-regulatory agencies of Canada and the European Union receive studies on bee effects and other pesticide hazards that were performed on behalf of product registrants, the manufacturers or others responsible for the pesticides. Based on evaluation of these studies, regulators decide whether a particular pesticide will be allowed for use (registered) within their jurisdiction and what instructions and precautions will be placed on product labels. Registrants' studies of pesticide effects are considered to be trade secrets and are not available for public review. Authors instead reviewed registration reports, which present the agencies' conclusions and summaries on registrants' studies.

    Canada, European Union, and U.S. EPA review and summarize many of the same registrant studies and provide differing perspectives on them. Based on the adequacy of available information and their differing evaluation criteria, the European Union has declined to register (allow use of) certain pesticides in Europe for which EPA allows use in the United States. Registration reports by EPA generally provide the least information on bee effects in comparison with registration reports from Canada and the European Union. In addition to studies provided by registrants, registration reports by the European Union cite and review studies in the open literature on the effects of pesticides on the honey bee, Apis mellifera, and other managed bee species, such as bumble bees, Bombus spp.

    Most registration reports of U.S. EPA do not cite or summarize any open literature on the bee effects of pesticides. Based on the information EPA says they reviewed and the content of their reports, for most registered pesticides the EPA appears to have

    • Considered only bee-effects studies provided by registrants.
    • Not considered studies on any bee species other than the non-native honey bee.

    The authors searched for bee-effects reports in databases of regulatory agencies as listed below and searched the open literature primarily using Google Scholar. We also reviewed the literature cited or references of pertinent studies to identify additional studies. We critically reviewed these reports and studies to assess the effects of pesticide active ingredients (common names) and (where available) formulated products (trade names, see question 9) on the adults and brood (immatures) of various bee species (family Apidae). Resources considered include

    • How to Reduce Bee Poisoning from Pesticides- 2016. Pacific Northwest Extension (PNW) publication PNW591.
    • U.S. EPA criteria for the pollinator precautionary statement (PDF) on pesticide labels. These historically have been based on the acute, contact and oral toxicity of active ingredient(s) to adult honey bees as determined by laboratory studies. These EPA criteria are LD50 (≤ 2 μg/bee, > 2 to < 11 μg/bee, or ≥ 11 μg/bee) and the residual (persistence of) toxicity to adult honey bees. Note that LD50 (lethal dose 50%) is the amount of pesticide applied in a single dose that on average kills one-half of the exposed bees during the length of the study, usually 48 hours. One microgram (μg) equals one millionth (0.000001) of a gram.
    • Websites of agencies that register and regulate pesticides:

    You can download a bibliography of reports and studies reviewed (PDF) as of 2018 by authors of the Bee Precaution Pesticide Ratings with links to those online.

  4. How did authors establish the ratings in the Bee Precaution Pesticide Ratings?

    Authors used others' agreed-upon or standard criteria for assessing the importance of pesticide effects on bees, when these were adequate and pertinent (see question 5) to the particular pesticide and how it is used in the field. For adult honey bees, according to U.S. EPA

    • An acute (within 48 hrs) LD50 ≥ 11 μg/bee for the active ingredient is considered not toxic to honey bees. The rating for such pesticides would be
      • III - No bee precaution, except when required by the pesticide label or regulations.
    • If acute LD50 < 11 μg/bee, the bee precaution is
      • II - Do not apply or allow to drift to plants that are flowering including weeds, except when the application is made between sunset and midnight if allowed by the pesticide label and regulations. Do not allow pesticide to contaminate water accessible to bees including puddles, or
      • I - Do not apply or allow to drift to plants that are flowering including weeds. Do not allow pesticide to contaminate water accessible to bees including puddles.

      Exceptions include soil-applied baits, which we generally rated III. These granules or pellets are not expected to cause significant pesticide exposure to honey bees if they do not drift (such as in pesticide-contaminated dust) or contaminate water accessible to bees (e.g., puddles).

    • For products of known toxicity to adult honey bees (LD50 < 11 μg/bee), rating I versus II is discriminated by EPA's RT25 criterion. Residual toxicity (RT) and 25 (= 25%) means the length of time post-application that the test substance on foliage kills 25% or less of adult honey bees during a laboratory study. At RT25, EPA no longer considers the pesticide to be toxic to honey bees. Where EPA provides such data, the mortality after application is reported at varying intervals, some combination of <, >, or = 1, 2, 3, 4, 5, 7, 8, or more hours.

    There are relatively few pesticides for which EPA knows and reports the Residual Time to 25% Bee Mortality (RT25). However, there are many open-literature studies on the half-life of pesticides after application, such as those summarized in Estimating Half-Lives for Pesticide Dissipation from Plants. These provide insight on how quickly pesticides may degrade and helped the authors decide whether bee-toxic pesticides should receive a precaution of I versus II.

    In addition to the registration reports of Canada, European Union, and U.S. EPA the authors reviewed studies available in the open literature on the acute, chronic, and residual toxicity of many pesticides to bumble bees, honey bees, and some other species, such as alfalfa leafcutting bee (Megachile rotundata) and alkali bee (Nomia melanderi). The authors critically considered the conclusions, findings, and methods of these studies, which commonly used differing considerations and criteria other than EPA's for concluding whether the pesticides tested are toxic to bees.

    Authors also reviewed reports of pesticide effects on brood (immature bees), most of which pertain to bumble bees or honey bees. The most specific guidelines on testing effects on brood are from the Organisation for Economic Co-operation and Development (OECD 2007, OECD 2016 PDFs). EPA (2016 PDF) also provides criteria and accepts those of OECD; the United States is a member of OECD.

  5. Isn’t following the label enough to protect bees? Why should I use the Bee Precaution Pesticide Ratings?

    Following the Bee Precaution Pesticide Ratings will sometimes be more protective of bees than just following the label. The tool sometimes advises not applying certain pesticides during some times that are allowed by the label. Pesticide users must take at least the minimum precautions required by the pesticide label and regulations. Users may also take more protective (restrictive) actions, such as those in the Bee Precaution Pesticide Ratings, if not prohibited by (in conflict with) the label or regulations.

    The EPA criteria (see question 4) may not be adequate or pertinent for the characteristics of certain pesticides and their use in the field. Examples include:

    • Bactericides, fungicides, and herbicides lack a pollinator precautionary statement (bee hazard warning) on their labels even though some are toxic to bees.
    • Demethylation inhibitor (DMI) fungicides (FRAC 3 e.g., propiconazole, tebuconazole, triflumizole) can increase (synergize) the bee toxicity of various insecticides including butenolides (IRAC 4D), diflubenzuron and other IRAC 15 growth regulators, neonicotinoids (IRAC 4A e.g., dinotefuran, imidacloprid, thiamethoxam), and pyrethrins and pyrethroids (IRAC 3A e.g., cyhalothrin, cypermethrin, permethrin). The DMI fungicides can increase the bee toxicity of insecticides because they disrupt bees' internal process for detoxifying poisonous chemicals. The EPA does not consider or require tests of pesticide synergism, and DMI fungicides lack a pollinator precautionary statement on their labels. Note that FRAC (Fungicide Resistance Action Committee) and IRAC (Insecticide Resistance Action Committee) followed by a number or letter-number combination refer to pesticide modes of action as discussed in question 11.
    • Explicit criteria are not provided for deciding when a pollinator precautionary statement must be placed on the labels of bee-toxic products that after application in the field are found to contaminate honey, nectar, pollen, or beeswax. Regulators provide guidelines on how to conduct and document the effects of pesticides on brood (OECD 2013, 2016; U.S. EPA 2016 PDFs). But they do not state when must restrictions be placed on the labels and use of such pesticides based on the particular results of brood studies.
    • Immature (developing) insects are affected by growth regulators, such as those inhibiting synthesis of chitin (IRAC 15 e.g., diflubenzuron and novaluron and IRAC 16: buprofezin); chitin comprises the body covering of insects. Pesticides designed to affect immatures or be toxic to insects in a delayed manner have not been adequately considered by EPA, which historically has required only tests of acute toxicity to adult bees.
    • Microbial insecticides composed of bacteria, fungi, or viruses can infect hosts and cause development of disease, which may not become apparent during EPA's 48-hr, LD50 test. According to regulators, microbial pesticides should be evaluated for infectivity and pathogenicity for a 28-day minimum after exposure (OECD 2003, 2004 PDFs) or at least 30 days after exposure (EPA 1996 PDF). For microbial pesticides registered by EPA, commonly no bee-effects studies conducted for such a lengthy period were presented in registration reports or found by authors in the open literature.
    • Systemic pesticides (e.g., neonicotinoids) can persist in plants for weeks to months and translocate (move within plants) after application to contaminate nectar and pollen. Bees may be repeatedly exposed to such widely used products, unlike with the EPA (2012 PDF) single-dose test and subsequent observation of bees limited to 48 hours.
  6. Does the rating of I, II, or III apply to all bee species or only the honey bee, Apis mellifera?

    The I to III ratings in the Bee Precaution Pesticide Ratings are for adults and brood of the honey bee.

    Most pesticide-registration reports of EPA (see question 3) in regards to bees

    • Cite or summarize only studies of adult honey bees.
    • Do not address honey bee brood.
    • Present no information on the adults or brood of other species of bees.

    Following the advice in Bee Precaution Pesticide Ratings and on pesticide labels may help to protect other bee species. However, there are several thousand species of bees in the United States and their susceptibility to pesticides and some methods for protecting them can differ in comparison with honey bees. For example, bee-toxic pesticides that will mostly degrade within a few hours after application commonly are rated

    • II - Do not apply or allow to drift to plants that are flowering including weeds, except when the application is made between sunset and midnight if allowed by the pesticide label and regulations. Do not allow pesticide to contaminate water accessible to bees including puddles.

    This reduces exposure and poisoning of honey bees because they spend the night protected in a hive, commonly a wooden box. Because some other bee species spend the night on plants or in soil at the site, they may not be protected by delaying pesticide application until nightfall.

    Consult Best Management Practices to Protect Bees from Pesticides, Conserving Bumble Bees, and Protecting Natural Enemies and Pollinators for more bee-protection guidance. Pesticide precautions for managed bumble bees, Bombus spp., are provided by Biobest (Side Effect Manual) and Koppert (Side Effects), which sell bumble bees for crop pollination. To help you identify what species of bees are present at a site, consult Farming for Bees: Guidelines for Providing Native Bee Habitat on Farms and the California website of the Pollinator Conservation Resource Center. To learn what bee species are important pollinators of particular crops, click the "Find a Crop" link at the top of Best Management Practices for Pollination.

  7. What does "Toxic to honey bee brood" mean? For example, why do many of the pesticides that are toxic to honey bees (rated I or II) lack a check mark (equals yes) in the column of toxicity to brood?

    The Bee Precaution Pesticide Ratings are for pesticide application in the field, and application to crops does not necessarily lead to pesticide exposure or poisoning of brood (bee eggs, larvae, and pupae). Brood occur in the hive or nest, which generally protects them from direct exposure to pesticides. Except for illegal practices, such as when hives or nests are directly sprayed or exposed to drift (airborne movement of pesticide off-target), exposure of brood is commonly a result of adults carrying pesticide into the hive or nest. An exception is when beekeepers apply pesticides to hives to control pests of honey bees, which include certain insects (e.g., hive beetles and wax moths), pathogens (foulbrood bacteria), and especially mites (Varroa destructor).

    Pesticides with high, acute toxicity to bees (rated I or II) include carbamates (IRAC 1A), organophosphates (IRAC 1B), and pyrethroids (IRAC 3A). Most of these do not have a check mark in the column of toxicity to brood because their proper application in the field generally is not expected to result in significant exposure of honey bee brood. Workers (adult bees) poisoned while gathering nectar, pollen, or water can be killed quickly or become unable to fly or navigate, and therefore may not return to contaminate the hive. Workers that collect food in the field pass it to nurse bees (other adults) in the hive, which internally process food before it is fed to honey bee larvae or the queen. This processing can help to degrade certain pesticides and limit poisoning of the brood or queen. Note that FRAC (Fungicide Resistance Action Committee) and IRAC (Insecticide Resistance Action Committee) followed by a number or letter-number combination refer to pesticide modes of action as discussed in question 11.

  8. Why are some pesticides listed more than once under different names (e.g., sulfur and sulphur)?

    Our goal is to helps users find the bee precaution rating using the pesticide name with which they are familiar. For many pesticides more than one name is used. For example, "sulfur" is the common spelling in American English, but "sulphur" is the spelling used by the European Union and Fungicide Resistance Action Committee (FRAC), the source of mode-of-action codes for bactericides, fungicides, and oomyceticides (see question 11).

  9. What is the difference between “common name” and “trade name”? How is it relevant to pesticide effects on bees?

    The names have different meaning. Knowing this difference is important to understanding the Bee Precaution Pesticide Ratings.

    The common name identifies the active ingredient. Active ingredients are chemicals known to have toxic effects on the target pest(s). For purposes such as pesticide registration (government approval to sell and use, see question 3) and use in publications, each pesticide active ingredient is assigned a nonproprietary, short, and widely accepted common name by the International Organization for Standardization.

    A trade name (brand name) is also placed on pesticide labels. This is the name given by the pesticide manufacturer or supplier. It is the most prominent name on product labels and is used in product advertisements. The trade name refers to the particular combination of the active ingredient(s) plus other ingredients added to the product, called the formulation. Manufacturers add other ingredients to improve pesticide application, handling, mixing, safety, and storage. These other ingredients do not necessarily have pesticidal action but may still pose environmental or safety problems. Pesticide labels list the products' percentage of active and other ingredients, and name all the active ingredients. However, manufacturers do not usually list the other ingredients in a pesticide product. Please consult Understanding Pesticide Labels for Making Proper Applications for more information.

  10. Does the type of formulation affect pesticide hazard to bees?

    Yes. Given the same active ingredient, certain formulations can be more hazardous to bees as summarized in the table below. Trade-name products (see question 9) with the same active ingredient (common name) can have different formulation types and other ingredients. The type of formulation may be identified on pesticide labels, sometimes by a one- to three-letter abbreviation (e.g., W or WP for wettable powder).

    Manufacturers do not publicly identify all the other ingredients in their products. These unidentified ingredients commonly comprise the largest percentage of formulated (trade-name) pesticides. Some of these other ingredients are toxic to bees, such as certain adjuvants (Artz DR & TL Pitts-Singer 2015, Chen J et al 2018, Ciarlo TJ et al. 2012, Mullen CA 2015, Mullen CA et al. 2016). The other ingredients cannot be confidently known by the authors and the Bee Precaution Pesticide Ratings generally do not discriminate (modify) ratings according to formulation type; exceptions include soil-applied baits as explained in question 4.

    Pesticide Formulations, their Relative Hazard to Bees, and Precautions to Reduce Hazard. Formulations are Ordered from the Most Hazardous to Bees at the Top to Less Hazardous at the Bottom.

    Formulation type (abbreviation)

    Bee exposure

    Precautions

    Dry flowable (DF), or water-dispersible granule (WDG)

    Dust (D)

    Flowable (F, a liquid), or liquid (L)

    Microencapsulated (M)

    Wettable powder (W, WP)

    Particles similar in size to pollen stick to bee hairs and can be taken to hives and fed to brood. Chemigation drips or puddles may attract bees.

    Consider using formulations less hazardous to bees (those below) if available for that active ingredient (common name). Avoid application during weather conditions that increase drift. Use good management practices for chemigation and Best Management Practices to Protect Bees from Pesticides.

    Emulsifiable concentrate (E, EC)

    Direct spray and residues.

    Ultralow volume (ULV) formulations may be more hazardous to bees than other liquid formulations. Use a less-hazardous active ingredient or formulation or both if feasible.

    Soluble powder (SP)

    Solution (S)

    Direct spray and residues. Chemigation drips or puddles may attract bees.

    Ultralow volume (ULV) formulations may be more hazardous to bees than other liquid formulations. Use a less-hazardous active ingredient or formulation or both if feasible. Use good management practices for chemigation and Best Management Practices to Protect Bees from Pesticides.

    Systemic (bark or soil injection or spray, chemigation, or foliar spray), absorbed and translocated (moved) within the plant

    Some systemic insecticides may translocate to guttation (plant exudate) droplets, nectar, and pollen and can be ingested by bees. Chemigation drips or puddles may attract bees.

    Delay application where feasible until after plants have completed their seasonal flowering. Use good management practices for chemigation and Best Management Practices to Protect Bees from Pesticides.

    Bait (B), granular or pellet

    Granular (GR)

    Pellet (P)

    Applied to soil. Honey bees do not pick up the pesticide granules or pellets and are unlikely to be exposed unless the application contaminates water (e.g., puddles) accessible to bees or generates pesticide dust that drifts.

    Avoid applying to soil near beds of ground-nesting bees, such as alkali bees. Do not allow pesticide to contaminate water accessible to bees including puddles. Prevent the formation and movement of pesticide-contaminated dust.

    Seed coatings and treatments

    Applied directly to seed. Ideally, exposure of honey bees is not expected. Note that certain seed treatments are systemic pesticides (e.g., neonicotinoids, see "Systemic . . ." above and question 5).

    When planting seed coated with pesticide-containing graphite or talc, older equipment and methods enable drift of the pesticide onto blooming crops or weeds or adjacent habitat. Use newer, seed-flow lubricants to help reduce pesticide drift and dust. Prevent the formation and movement of pesticide-contaminated dust.

    Adapted from How to Reduce Bee Poisoning from Pesticides, Pacific Northwest Extension publication PNW591 and Forestry and Right-of-Way Pest Control, University of California (UC) Agricultural and Natural Resources (ANR) publication 3336.

  11. Why are mode-of-action (MOA) codes presented?

    Mode of action refers to the way a pesticide's active ingredient (common name) affects or kills targeted organisms (pests). Each MOA is assigned a distinguishing code that may be presented on pesticide labels. The main purpose of the mode-of-action codes is to help users identify the appropriate pesticide rotations (alternations) to prevent the development of pesticide resistance. This helps maintain the effectiveness of pesticides.

    The source of MOA classifications for acaricides (miticides) and insecticides is the Insecticide Resistance Action Committee (IRAC). The MOA codes for bactericides, fungicides, and oomyceticides are provided by the Fungicide Resistance Action Committee (FRAC). Herbicide MOA codes are developed by the Herbicide Resistance Action Committee (HRAC) and Weed Science Society of America (WSSA).

    Knowing the MOA can also help to protect bees. Mixing pesticides together that have certain modes of action can increase (synergize) toxicity to bees. For example, mixing a pyrethroid insecticide (IRAC MOA code 3A e.g., cyhalothrin, cypermethrin, and permethrin) with the fungicide chlorothalonil (FRAC M5) may increase toxicity to bees. Exposure to demethylation inhibitor (DMI) fungicides (FRAC 3 e.g., propiconazole, tebuconazole, and triflumizole) can increase the bee toxicity of many insecticides (see question 5) because DMI fungicides disrupt bees' internal process for detoxifying poisonous chemicals. Conversely, some modes of action generally are not expected to be toxic to bees because they specifically target plants (weeds) or invertebrate types such as mites.

    Fungicide MOA codes refer to how fungi are affected, herbicide codes are based on how plants are affected, and so on. IRAC's MOA codes indicate how insects are affected, but do not reliably indicate toxicity to bees. For example, if a systemic neonicotinoid (IRAC 4A) application is planned, the bee precaution for these active ingredients is I or II depending on which active ingredient is chosen. The acute toxicity of neonicotinoids to bees differs by more than 100×; acetamiprid (rated II) is the least toxic to bees; clothianidin, imidacloprid, and thiamethoxam are the most toxic (rated I).

  12. What is the explanation of presentation style for mode-of-action (MOA) codes and pesticide types for premixes (pesticide combinations)?

    Premixes are formulations (trade-name products, see question 9) to which the manufacturer has added two or more pesticide active ingredients. Each active ingredient (common name) may be of more than one type (e.g., both a fungicide and insecticide) and so have more than one mode-of-action code (see question 11). For example, the types and MOA presentation for the premix pyridaben/sulfur (trade name: Desperado) is presented below.

    For each pesticide type, two numbers representing MOA are presented in the respective order of the active ingredients separated by a forward slash (/). What the presentation may not adequately convey is that pyridaben is an acaricide and insecticide (two types, both IRAC 21A), while sulfur is an acaricide, fungicide, and insecticide (three types, IRAC UN and FRAC M2). Therefore, the correspondence between pesticide names, types, and modes of action sometimes is confusing.

    For certain premixes, the presentation style is more clear because the pesticides are of the same type and mode of action. For example, the premix of 2,4-D/dicamba/MCPP (Trimec) contains three active ingredients with the same HRAC and WSSA mode-of-action codes, O·4 (where O is the HRAC mode-of-action code and 4 is the WSSA code). Note that instead of presenting the codes for 2,4-D/dicamba/MCPP as O·4/O·4/O·4, when the product is a premix of more than one active ingredient all of the same type and the same MOA, the codes are presented only once as below.

  13. Why don't all herbicides have the "other effects on bees" or "indirect" note?

    Because a bee precaution of I or II already conveys concern about the pesticide, the "indirect" note is presented only for herbicides rated III. According to the available information, herbicides primarily harm bees indirectly by reducing the availability of flowering plants that produce nectar, pollen, and bee nesting material. The "indirect" note is presented so users would not get the impression that application of herbicides rated III cannot affect bees.

  14. Why is the pesticide I am looking for not listed?

    Make sure that you have the correct spelling. If you're searching for a trade name (brand name), most are not listed; learn and look for the common name, the name of the product's active ingredient (see question 9). The names listed are primarily the common name of active ingredients in the UC IPM Pest Management Guidelines for commercial agriculture.

Technical Questions

  1. Why does choosing "All types" (the default) in the box near the top, then clicking "Add to list" not work?

    This is a limitation of our presentation from database. To display all of the pesticide ratings you must one at a time select each of the ten types from the drop-down list in the first box. For example, select "Acaricide" in the first box, then after "All Acaricides" appears in the second box, click "Add to list" at the right. Next, select "Bactericide," "All Bactericides" appears, click "Add to list," and so on.

    Certain active ingredients are multiple types of pesticide. For example, selecting only fungicides will list the acaricides, bactericides, and insecticides that are also fungicides. Some active ingredients are of only one type, such as herbicides. Currently the only way to see all of the rated pesticides is to select each of the ten types one at a time.

  2. Why doesn't sorting by trade name work, even when I select the "Trade name" button?

    The button affects only the search, meaning whether the second drop-down box lists common names or trade names. Except for soil-applied baits as explained in question 4, the ratings are for the active ingredient (common name) and not for specific products (trade names, see question 9). Therefore the database will associate and sort the information according to the pesticide common name.

  3. How can I download all the results of interest to me?

    Downloading listed ratings is not currently available. An alternative is to use a personal computer to view the Bee Precaution Pesticide Ratings and print or save them as a PDF from your web browser.

Learn about how to use the Bee Precaution Pesticide Ratings video. [3:05]

Text Updated: 05/21