Exposure of Honey Bees to Pesticides 

and the Relative Importance of the 

Identified Exposure Routes

U.S. Environmental Protection Agency 1

Christina Wendel, M.S.

Environmental Fate and Effects Division

Office of Pesticide Programs
Outline

• Discussion of the potential exposure routes/pathways by 

application type and age of the bee (adult worker vs. larvae) 

• Foliar Applications

• Soil Applications & Seed Treatments

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• Exposure pathways considered and included in the Tier I 

exposure assessment

• Exposure pathways considered but not included in the Tier I 

exposure assessment
Potential Exposure Routes for Honey Bees

• Contact 

• Direct spray, contaminated foliage and soil, dust, comb wax, propolis, 

and/or pollen

• Oral

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• Oral

• Dietary 

• Pollen, nectar, honey, bee bread, royal jelly, and/or brood food

• Drinking water

• Ponds, puddles, dew, and/or guttation fluid

• Inhalation 

• Spray droplets, and/or volatilized chemical
Foliar Spray Applications – Exposure Routes

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Contact: 

Direct spray

Oral: Collection 

and consumption 

Adult Forager 

Bees

Inhalation: Spray

droplets or 

Contact: With contaminated 

foliage, soil, comb wax, 

propolis and/or pollen

Oral: Collection 

and consumption 

of contaminated 

pollen, nectar, 

and/or drinking 

water

droplets or 

gaseous phase of 

chemical
Foliar Spray Applications – Exposure Routes

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Oral: Processing 

and consumption 

Hive Bees

(Adults and Larvae)

Inhalation: 

Contact: With contaminated 

comb wax, propolis and/or 

pollen

Oral: Processing 

and consumption 

of contaminated 

pollen, nectar, 

and/or drinking 

water

Inhalation: 

Gaseous phase of 

chemical
Soil and Seed Treatment Applications –

Exposure Routes

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Oral: Collecting, 

processing, and 

Forager bees and in hive 

bees (adults and larvae)

Inhalation: 

Contact: With contaminated 

dust, comb wax, propolis

and/or pollen

Oral: Collecting, 

processing, and 

consumption of 

contaminated 

pollen, nectar, 

and/or drinking 

water

Inhalation: 

Gaseous phase of 

chemical
Exposure Pathways in the Tier I Screen

• Contact with

• Direct spray,

• Contaminated foliage, soil, comb wax, propolis, and/or pollen

• Dust

• Oral

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• Oral

• Dietary 

• Pollen, nectar 

• Honey, bee bread, royal jelly, and/or brood food

• Drinking water

• Ponds, puddles, dew, and/or guttation fluid

• Inhalation 

• Spray droplets, and/or gaseous phase of a volatilized chemical
Contact Exposure - Dust

• Potential major route of exposure for some pesticides and 

application scenarios

• Incidents of bee mortality related to dust exposure

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• Rationale of not including this exposure route into Tier I screen 

for all pesticides

• Effective quantitative screening tool is not currently available

• Stewardship Programs

• Management of exposure through mitigation

• BMP’s

• Seed coating technologies

• Alternative lubricating agents to talc and/or graphite
Oral Exposure – Drinking Water

• Compared potential doses received through contact (direct 

spray) and oral (dietary) versus contaminated drinking water 

• Ponds and Puddles

• Discountable relative to contact and dietary routes of exposure

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• Discountable relative to contact and dietary routes of exposure

• Dew and Guttation fluid

• Potentially significant based on conservative assumptions

• Investigated further
Dew and Guttation Fluid

Exposures are not expected to be as significant when compared 

to diet because of two primary reasons

1. Time of day when available vs. foraging times for bees

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2. Consumption rates from water vs. food
Estimated amounts of water consumed from food for adult bees

Worker Task

Honey Nectar

Percent daily water flux 

consumed with food

Percent daily water flux 

consumed with food

Cell cleaning and capping 8% 84%

Brood and queen tending 

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Brood and queen tending 

(nurse bees) 22% 234%

Comb building, cleaning 

and food handling 8% 84%

Foraging (pollen) 7% 73%

Foraging (nectar) 38% 409%
Inhalation Exposure

• Highly volatile pesticides

• i.e., fumigants

• Foliar and Soil applications

• Not relevant for seed treatment applications

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• Not relevant for seed treatment applications

• Hives in close proximity to treated site

• Currently evaluating the inhalation exposure pathway. 

Preliminary results suggest that exposure from inhalation is 

substantially lower than the dietary or contact exposure. 
Summary of Pathways Considered

• Focused on routes that create the most substantial exposures 

• Primary (major) routes of exposure:

• Contact - via direct spray, contact with contaminated dust – on a case by 

case basis

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• Oral - via Pollen and Nectar (assumed to be protective of honey, bee 

bread, royal jelly, brood food)

• Other routes of exposure:

• Contact via contact with contaminated foliage, soil, comb wax, propolis, 

and/or pollen

• Oral via consumption of contaminated drinking water

• Inhalation