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 https://extension.oregonstate.edu/catalog/pub/pnw-591-how-reduce-bee-poi....
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 (Figure 1). This activity is economically significant for both farmers and beekeepers from Washington, Idaho and Oregon, who derive the bulk of their income from colony rentals, as opposed to honey production.
While honey bees are the most economically important pollinators, two other managed bees are of importance to maintaining alfalfa seed production in the region. These are the alfalfa leafcutting bee (Megachile rotandata) and the alkali bee (Nomia melanderi). To a lesser extent growers of tree fruits have been using the solitary orchard mason bee (Osmia lignaria) to supplement honey bee pollination. In addition, the region is home to almost 1,000 species of native bees, a subset of which live in and around agricultural fields. Wild bees contribute to crop pollination, with the most prominent in our region being wild bumble bees, which can provide significant pollination in red clover seed and cranberry.
Rules to protect bees
READ THE PESTICIDE LABEL (Fig 2). Specific precautionary statements designed to protect bees are found in the Environmental Hazards section of the pesticide label, with restrictions or required mitigations listed under Specific and General Use Directions sections. Review the entire label for precautionary advisory statements or restrictions. Products that are acutely toxic to bees will contain the words “highly toxic to bees” or “toxic to bees” (Fig. 2.2) and should be used around bee-attractive bloom with considerable caution. Some bee-toxic pesticides dissipate over the course of an evening and can be used at full bloom if sprayed at dusk when bees have returned to their hive. These products will have the following language under Environmental Hazards “do not apply this product or allow it to drift to blooming crops if bees are actively foraging in the treatment area”. Pesticides that remain toxic through the following morning will have a similar statement, but will be missing the word “actively”. Some pesticide products will list the specific time taken for toxicity to dissipate to a point where fewer than 25% of bees will be killed and this time may be listed in terms of RT25 (i.e., a product with an RT25 value of <8 hours can be treated at dusk and dissipate sufficiently to be of minimal risk to foraging bees).
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. A new tiered risk assessment for honey bees evaluates the effect of nectar and pollen contamination and will lead to new required mitigations that will be visible under the Specific Use directions of the pesticide label.
General mitigation measures to protect pollinators
Understanding pesticide label information on the hazard and risks of bees is an important first step to protecting bees. Insecticides and some fungicides are of concern for bees. Here are a few general actions to help minimize pesticide exposure to bees while managing pests and diseases.
1. Avoid sprays during bloom when possible. Bees face the highest exposure when pesticides are applied to the bloom of bee-attractive crops and weeds. When possible, use sprays before bloom to control pests and diseases to reduce the need for treatments at bloom.
2. If you must treat during bloom, choose products carefully and apply in the evening. Choose insecticides that are not labeled as “Toxic” or “Highly Toxic” to bees (Fig 2.2). Avoid insecticides where residues remain toxic to bees for longer than 8 hours (Fig 2.3). Always look to the Directions for Use for more specific information on when a product can be applied at reduced risk to bees (Fig 2.4)
3. Cooperate and communicate with beekeepers in a timely manner. Contact beekeepers at least 48 hours prior to applying insecticides or fungicides to blooming bee-attractive crops. The beekeeper may choose to cover or move colonies, or may leave colonies in place depending on the toxicity of the product being sprayed.
4. Avoid spraying bee colonies and bee habitat. Avoid placing bees directly in the crop. In cases where colonies can only be set in the crop, turn sprayers off as you pass over the colonies. Reduce drift onto adjacent flowering habitat by using coarser droplet sizes, drift reducing agent, or intelligent sprayer technology.
5. Mow blooming weeds. If there are bee-attractive blooming weeds (e.g., mustard, clover or dandelion), mow them before spraying.
6. Review Pollinator Protection Plans and use IPM. Oregon, Washington and Idaho have state plans that provide information on how to protect bees and other pollinators. Contact your Department of Agriculture to obtain these plans. Integrated Pest Management (IPM) can also reduce bee pesticide exposure. Contact your regional IPM Center for details.
State initiatives to protect pollinators
The state agriculture departments in Oregon, Washington, and Idaho are the most reliable sources of guidance 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.”
Oregon:
- Apiary Registration: www.oregon.gov/ODA/programs/IPPM/InsectsSpiders/Pages/BeesApiaries.aspx
- Pollinator Issues web page: www.oregon.gov/ODA/programs/Pesticides/Pages/PollinatorIssues.aspx
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. 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. It is important to contact your state Department of Agriculture as soon as you notice a problem.
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
- Email: pestx@oda.state.or.us
- Phone: 503-986-4635
- Process for Investigating Pesticide Complaints: www.oregon.gov/ODA/programs/Pesticides/Pages/PesticideComplaints.aspx
Washington State Department of Agriculture
- Pesticide Management Division
- Email: pcompliance@agr.wa.gov
- Phone: 360-902-2040 or 877-301-4555 (toll free)
- Process for Investigating Pesticide Complaints: agr.wa.gov/PestFert/Pesticides/docs/566-PesticideComplaintInvestigationProcess.pdf
Idaho State Department of Agriculture
- Agricultural Resources Division
- Email: pesticidecompliance@isda.idaho.gov
- Phone: 208-332-8605
- Process for Investigating Pesticide Complaints: agri.idaho.gov/main/56-2/pesticides/enforcement/enforcement-2/
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: www.epa.gov/pollinator-protection/report-bee-kills
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, diazinon, dimethoate, malathion, and methamidophos)
- N-methyl carbamates (such as carbaryl)
- Systemic neonicotinoids (such as clothianidin, dinotefuran, imidacloprid, and thiamethoxam)
- Pyrethroids (such as bifenthrin, 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
Some signs and symptoms of bee poisoning can be difficult to distinguish from non-pesticide related problems with the hive. Nevertheless, colonies that have been poisoned may exhibit any of the following:
- 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
- Stupefaction, paralysis, and abnormal jerky, wobbly, or rapid movements; spinning on the back
- Forager disorientation and reduced foraging efficiency
- Immobile, lethargic bees unable to leave flowers
- Regurgitation of honey stomach contents and tongue extension
- Performance of abnormal communication dances, fighting or confusion at the hive entrance
- The appearance of “crawlers” (bees unable to fly). Bees slow down and behave as though they have been chilled
- Poor brood development, with adult bees unaffected
- Dead brood, dead newly emerged workers, or abnormal queen behavior, such as egg laying in a poor pattern
- Queenless hives
- Poor queen development in colonies used to produce queens, with adult bees unaffected
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 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): https://extension.oregonstate.edu/catalog/pub/pnw-591-how-reduce-bee-poi...
UC IPM / Bee precaution pesticide rating: https://ipm.ucanr.edu/bee-precaution-pesticide-ratings/