How to Reduce Bee Poisoning from Pesticides

Erik Johansen and Judy Wu-Smart
Latest review—March 2021

Substantial portions of this article are taken from How to Reduce Bee Poisoning from Pesticides (PNW 591), written by Louisa Hooven, Ramesh Sagili and Erik Johansen. The publication may be downloaded as a pdf or an app:

Pollinators are essential to Pacific Northwest agriculture

Commercially managed honey bees pollinate a variety of crops in the Pacific Northwest, including tree fruits, berries, cucurbits, and crops grown for seed. This activity is economically significant. Beekeepers from California and the Pacific Northwest together perform nearly half of the nation’s commercial pollination, valued at approximately $18 billion (Calderone 2012).

While honey bees are the most economically important pollinators, other managed bees are important as well. For example, alfalfa seed production in the western United States is dependent on alfalfa leafcutting bees and alkali bees for pollination, and managed bumble bees are important for greenhouse tomato production and some covered row crops. Native wild (pollen) bees, including numerous species of bumble bees, mining bees, mason bees, sweat bees, leafcutting bees, and carpenter bees, are all prolific pollinators. The estimated annual value of crops pollinated by wild, native bees in the U.S. is $3 billion or more (Losey and Vaughan, 2006, Chaplin-Kramer et. al. 2011). More than 1,600 species of bees are native to California, Idaho, Oregon, and Washington (Tepedino and Griswold 1995; U.S. Pollinating Insects Database 2013). The full value of their pollination services to increased crop production is substantial, even in the presence of honey bees (Garibaldi et al. 2013), but their sensitivity to pesticides has not been studied extensively.

Rules to protect bees

READ THE PESTICIDE LABEL. Specific precautionary statements designed to protect bees are usually found in the Environmental Hazards section of the pesticide label. Some pesticide labels may include a bee advisory box and a bee hazard icon to more clearly identify the pesticide’s potential hazard to bees. Review the entire label for precautionary and advisory statements. Key words to look for include “highly toxic to bees,” “toxic to bees,” and “residues.” Crop-specific precautions may also be listed on the label. Although these precautions are based on toxicity to honey bees, they are also relevant to other species of bees, with some exceptions as noted in How to Reduce Bee Poisoning from Pesticides (PNW 591).

Residual toxicity to bees varies greatly among pesticides, and can range from hours to a week or more. When using insecticides with extended residual toxicity (residues expected to cause at least 25 percent mortality more than 8 hours after application), it is imperative that applicators and growers carefully consider potential exposures to both wild and managed bees, and avoid applying pesticides to blooming plants (crops or weeds). Residual toxicity data for some active ingredients is available on the EPA Pollinator Protection web page at

Systemic pesticides and the off-target movement of pesticide residues can increase potential exposure risks to bees. Systemic insecticide and fungicide residues may be translocated to all parts of a treated plant, including in the pollen and nectar where foraging pollinators may become exposed. Systemic pesticide residue contaminates in soil and water may also be taken up by surrounding vegetation. Therefore, utilizing chemical options that are less likely to leach into water supplies or are not persistent in soil will reduce the likelihood of off-target movement and non-target effects. Examine labels for Environmental Hazard Statements regarding the Soil Partition Coefficient and Aerobic Soil Metabolism Half-Life Phases as indicators of leeching and persistence potential.

Soil Partition Coefficient Phases

Specific Label Language

Leaching Potential

Kd less than 15

“high potential for reaching surface water via runoff”

Lower, possible surface water concerns

Kd between 15-300

“a medium potential for reaching both surface water and aquatic sediment via runoff”


Kd greater than 300

“high potential for reaching aquatic sediment via runoff”

High, possible ground water concerns

Aerobic Soil Metabolism Half-Life Phases

Specific Label Language

Persistence Potential

t1/2 less than 8 days

“several days after application”


t1/2 between 8 and 30 days

“several weeks after application”


t1/2 greater than 30 days

“several months or more after application”


The U. S. Environmental Protection Agency (EPA) is currently revising the risk assessment data requirements and process for pollinators, and it is expected that the precautionary statements on the labels of newly registered pesticides will be based on the results of these risk assessments. Potential chronic hazards to honey bees, and other pollinating insects, and the resulting label language will be assessed by the EPA on a case-by-case basis. The EPA is in the process of developing chronic toxicity label statements for pollinator protection. Refer to the EPA Pollinator Protection web page for additional information.

State rules to protect pollinators

The state agriculture departments in Oregon, Washington, and Idaho are the most reliable sources of current rules intended to reduce the hazard of pesticide applications to bees. For more information, call the number listed for your state under “Investigating and documenting a suspected bee poisoning incident.”



  • Apiary Registration:
  • General Pesticide Rules regarding Pollinator Protection (WAC 16-228-1220(1), WAC 16-228-1262 thru 1266):
  • Managed Pollinator Protection Plan (MP3):
  • MP3 for Alfalfa Seed Production:


  • Apiary Registration:
  • Idaho Administrative Code, Pesticide and Chemigation Use and Application Rules:

Investigating and documenting a suspected bee poisoning incident

If you have a question or concern regarding a suspected bee poisoning incident, contact your state agriculture department or, your county agricultural commissioner. Provide photos or video of the incident, together with notes describing the previous health of the colony, prevailing wind, EPA registration number (from the pesticide label) name of the suspected pesticide, how you believe the bees may have been exposed, pesticide treatments you have applied to the hives, and other pertinent details. Preserving at least 2 ounces of adult bees, brood, pollen, honey, nectar, or wax by immediately freezing in clearly labeled, clean containers may be helpful if the incident is later determined to warrant laboratory analysis.

In the event of enforcement action, some states will need to collect their own samples. Do not disturb the hives or site until the representative from your state lead office listed below has finished collecting information.

Oregon Department of Agriculture

Pesticide Division


Phone: 503-986-4635

Process for Investigating Pesticide Complaints:

Washington State Department of Agriculture

Pesticide Management Division


Phone: 360-902-2040 or 877-301-4555 (toll free)

Process for Investigating Pesticide Complaints:

Idaho State Department of Agriculture

Agricultural Resources Division


Phone: 208-332-8605

Process for Investigating Pesticide Complaints:

Report the bee poisoning incident to the EPA

The EPA requires multiple reports from beekeepers to detect any potential patterns related to specific pesticides. You can also notify the pesticide company, which is required by law to report adverse effects to the EPA.

Report a bee poisoning incident to the EPA:

Causes of bee poisoning in the Pacific Northwest

Highly toxic insecticides with residual toxicity longer than 8 hours are responsible for most of the bee poisoning incidents reported on the West Coast, primarily those in the following chemical families:

  • Organophosphates (such as acephate, chlorpyrifos, diazinon, dimethoate, malathion, and methamidophos)
  • N-methyl carbamates (such as carbaryl)
  • Systemic neonicotinoids (such as clothianidin, dinotefuran, imidacloprid, and thiamethoxam)
  • Pyrethroids (such as cyfluthrin, deltamethrin, and lambda-cyhalothrin)

Some pyrethroids (such as esfenvalerate and permethrin) are repellent to bees when used under arid conditions prevalent in eastern Oregon, eastern Washington, and Idaho. Repellency reduces the potential for bee poisoning from these insecticides under arid conditions, but they are likely to pose a hazard to bees when used in humid areas.

Most bee poisoning incidents occur when:

  • Beekeepers and growers do not adequately communicate.
  • Insecticides are applied when bees are foraging.
  • Insecticides are applied to bee-pollinated crops during bloom.
  • Insecticides are applied to blooming weeds in orchards or field margins.
  • Insecticides drift onto blooming plants adjacent to the target crop.
  • Bees collect insecticide-contaminated pollen (such as corn), nectar (such as cotton or mint), or other materials from treated crops that do not require bee pollination.
  • Bees collect insecticide-contaminated nectar from plants treated with systemic pesticides.
  • Bees collect insecticide-contaminated nesting materials, such as leaf pieces collected by alfalfa leafcutting bees.
  • Bees collect insecticide-contaminated water (from drip tape or chemigation, for example).

Pesticide poisoning isn’t always obvious and may be confused with other factors. Delayed and chronic effects, such as poor brood development, are difficult to link to specific pesticides, but are possible when stored pollen, nectar, or wax comb become contaminated with pesticides. Severely weakened or queenless colonies may not survive the winter.

Poisonous plants such as California buckeye (Aesculus californica), death camas (Toxicoscordion venenosum), cornlily (Veratrum viride), and spotted locoweed (Astragalus lentiginosus) can injure and occasionally kill bee colonies. Viral paralysis disease, starvation, winter kill, and chilled brood can cause symptoms that may be confused with bee poisoning. Beekeepers may request a laboratory analysis of dead bees to determine if pesticides were responsible for an incident. State agriculture departments in Oregon, Washington, and Idaho investigate suspected bee poisoning incidents.

Signs and symptoms of bee poisoning

Honey bees

  • Excessive numbers of dead and dying honey bees in front of the hives
  • Increased defensiveness (most insecticides)
  • Lack of foraging bees on a normally attractive blooming crop (most insecticides)
  • Stupefaction, paralysis, and abnormal jerky, wobbly, or rapid movements; spinning on the back (organophosphates and neonicotinoids)
  • Forager disorientation and reduced foraging efficiency (neonicotinoids)
  • Immobile, lethargic bees unable to leave flowers (many insecticides)
  • Regurgitation of honey stomach contents and tongue extension (organophosphates and pyrethroids)
  • Performance of abnormal communication dances, fighting or confusion at the hive entrance (organophosphates)
  • The appearance of “crawlers” (bees unable to fly). Bees slow down and behave as though they have been chilled (carbaryl)
  • Poor brood development, with adult bees unaffected (novaluron and spirodiclofen)
  • Dead brood, dead newly emerged workers, or abnormal queen behavior, such as egg laying in a poor pattern (carbaryl)
  • Queenless hives (acephate, carbaryl, malathion)
  • Poor queen development in colonies used to produce queens, with adult bees unaffected (coumaphos)

Honey bee recovery from pesticide poisoning

If a honey bee colony has lost many of its foragers, but has sufficient brood and adequate stores of uncontaminated pollen and honey, it may recover without any intervention. Move bees to a pesticide-free foraging area if available. If sufficient forage is unavailable, feed them with sugar syrup and pollen substitute, and provide clean water to aid their recovery. Protect them from extreme heat and cold, and, if needed, combine weak colonies.

If the pesticide has accumulated within pollen or nectar stores, brood and workers may continue to die until the colony is lost. Many pesticides readily transfer into beeswax, and you may consider replacing the comb with new foundation, drawn comb from unaffected colonies, or shaking the bees into a new hive and destroying the old comb and woodenware. Replacing brood comb on a regular schedule (typically 3 to 5 years) may prevent accumulation of pesticides to deleterious levels in brood comb wax.

Managed solitary bees

A distinctive sign of poisoning in alfalfa leafcutting bees is an inordinate number of dead males on the ground in front of a shelter or a lack of nesting activity by the females. Female alfalfa leafcutting bees usually forage within a few hundred yards of the field shelter, so the shelters closest to the source of the insecticide are more severely affected.

Pesticide poisonings are more difficult to detect in alkali bees, but watch for a lack of activity at the nesting beds or more dead males than expected. The males tend to spend most of their time at the nesting sites, so that may be your first clear sign of mortality. Females are more likely to die in the field. Female alkali bees forage up to a mile or more away from the alkali bee bed, so they can be killed by insecticides that male bees do not contact. An alkali bee bed without females often will have male bees flying in circles above the surface for several days after the poisoning incident.

Bumble bees and non-managed native bees

Without a marked hive or nesting site, pesticide poisonings in wild bees can easily go unobserved. Bumble bees and other wild bees experience many of the same symptoms of pesticide exposures as managed bees. Bumble bee colonies are composed of fewer individuals than honey bees and can be more sensitive to pesticides. Additional research is needed to fully understand the impact of pesticides on native bee populations, some of which are showing large population declines and even going extinct.

For information on bumble bee declines, see

Ways to reduce bee poisoning

Beekeeper–grower cooperation is the most effective way to reduce bee poisoning; its importance cannot be overstated. The underlying cause of most bee poisoning incidents is a lack of awareness, rather than an intent to do harm. Most pest control programs can be modified so that little or no bee poisoning occurs, without undue cost or inconvenience to the grower. Both beekeepers and growers benefit from developing working relationships and familiarizing themselves with each other’s management practices. Discussions and contracts between growers and beekeepers should include:

  • Coordination of crop timing with dates of apiary arrival and departure
  • Details of the beekeeper’s responsibility to provide strong, effective colonies for crop pollination
  • Details of the grower’s responsibility to safeguard bees from poisoning
  • Agreement on who is responsible for providing supplemental water and feed
  • Pest management practices in the cropping system before colonies are delivered
  • Pesticides to be used on a crop while beehives are present
  • Buffers between treated areas and apiaries
  • Informing neighboring growers and applicators of apiary locations
  • Possible pesticide use in adjacent crops
  • Location of honey bee colonies. Registering colonies with your state agriculture department or pesticide regulation department may help to improve communication between pesticide applicators and beekeepers.

For more information regarding active ingredients of commonly used pesticides and their effect on bees

Specific information regarding active ingredients of commonly used pesticides and their effect on bees:

How to Reduce Bee Poisoning from Pesticides (PNW 591):

UC IPM / Bee precaution pesticide rating: