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Pesticides and Honey Bees

Eric MussenExtension ApiculturistEntomology and NematologyUC Davis

Value of Honey Bees to California Commercial Agriculture

• Honey bees are rented to pollinate nearly 100 crops in California▫ Fruit, vegetable, nut and seed crops▫ The farm gate value exceeds $6 billion• Honey bee-pollinated crops make up about 1/3 of

the normal U.S. diet• We are having a hard time keeping our colonies

alive▫ No single cause, just too many sublethal stresses

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Major Topics to be Covered

• Definition of “Pesticide”• Pesticide Modes of Action• Determining Toxicity of Pesticides to Honey Bees• Detoxification of Pesticides• Pesticide Residues in Beehives• Exposure of Honey Bees to Pesticides• Avoiding Pesticide Exposure

Definition of “Pesticide”

• According to the U.S. Environmental Protection Agency (EPA): “A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.” • According to the California Department of Pesticide

Regulation (DPR): “Any substance or product that the user intends to be used for pesticidal poison purposes.”

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Definition of “Pesticide”

• California regulations also cover disinfectants, repellents, wood preservatives, pheromones, attractants, and plant growth regulators• Any word ending in “-cide” means kill:▫ insecticide, herbicide, homicide, genocide

Modes of Action(How Pesticides Kill)

• Pesticides are chosen or designed to interfere with metabolism:▫ the sum of the chemical reactions that take place

within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material

• Animals, plants, fungi, and bacteria rely on their metabolism to live

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Metabolic Pathways of Live Organisms

Metabolic Pathways of Live Organisms

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Sites of Biochemical Interference

chemistrypictures.org

Sites of Biochemical Interference

en.wikpedia.org

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Classifications of Pesticides

• By type (target pests)▫ Algicides, antifouling agents, antimicrobials,

attractants, biopesticides, biocides, defoliants, desiccants, disinfectants and sanitizers, fungicides, fumigants, herbicides, insecticides, insect growth regulators, miticides, microbial pesticides, mollusci-cides, nematicides, ovicides, pheromones, plant growth regulators, repellents, and rodenticides

Classification of Insecticides

• By mode of action▫ Group 1A – acetylcholine esterase inhibitors Carbamates: carbaryl (Sevin®), carbofuran (Furadan®)

(of 25)▫ Group 1B – acetylcholine esterase inhibitors Organophosphates – chlorpyrifos (Lorsban®),

malathion, parathion (of 64)▫ Group 2A – GABA-gated chloride channel

antagonists – chlordane, lindane, endosulfan

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Classification of Insecticides

• By mode of action▫ Group 2B – GABA-gated chloride channel

antagonists – fipronil (Maxforce® cockroach and ant baits; Frontline Flea and Tick Control®)

▫ Group 3 – sodium channel modulators – DDT and methoxychlor – Pyrethrins and pyrethroids: Pyganic®

(organic sprays), esfenvalerate (Asana®), fluvalinate (Apistan®), permethrin (bug-repellent clothing)

Classification of Insecticides

• By mode of action▫ Group 4A – nicotinic acetylcholine receptor

agonists/antagonists – imidacloprid, clothianidin, thiamethoxam and dinotefuran are “nitro-substitued” and much more toxic to honey bees than the “cyano-substituted” acetamiprid and thiacloprid

▫ Group 4B – nicotinic acetylcholine receptor agonists/antagonists – nicotine

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Classification of Insecticides

• By mode of action▫ Group 5 – nicotinic acetylcholine agonists (allosteric;

not Group 4) – spinosad (many homeowner organic products)

▫ Group 6 – chloride channel activators – abemectin(Agri-Mek® and Zephyr®)

▫ Group 7A – juvenile hormone mimics – hydroprene (Frontline Plus® for fleas on dogs) and methoprene (Precor® flea home spray)

Classification of Insecticides

• By mode of action▫ Group 7B and 7C – juvenile hormone analogues –

fenoxycarb and pyripoxyfen (Advantage® and K9 Advantix® “Spot On” flea products)

▫ Group 11A,B,C – microbial disruptors of insect midgut membranes – Bacillus thuringiensis strains Group 15 – inhibitors of chitin biosynthesis: type 0 = caterpillars diflubenzuron (Dimilin®)

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Classification of Insecticides

• By mode of action▫ Group 18A – ecdysone agonists/molting disruptors –

tebufenozide (Gorsem®)▫ Group 18B – ecdysteroid receptor antagonist –

azadirachtin (neem)▫ Group 19 – octopaminergic agonist - amitraz

(Miticur®, Taktic®, Mitac®, Ovasyn®, Apivar®)▫ Group 21 – mitochondrial complex IV electron

transport inhibitors – fenproximate (Hivastan®), rotenone

Classification of Insecticides

• By mode of action▫ Group 22 – voltage-dependent sodium channel

blockers – indoxicarb (Steward®), sabadilla▫ Group 23 – inhibitors of lipid synthesis –

spirodiclofen (Envidor®) and spiromesifen (Judo®)▫ Group 27A P450-dependent monooxygenase

inhibitors – piperonyl butoxide (PBT)

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Classification of Insecticides

• By mode of action▫ Group 28 – ryanodine receptor modulators –

flubendiamide (Belt®)▫ Botanical and fungal pesticides Some of the most toxic pesticides to insects Beauveria bassiana grows fast and eliminates other

microbes chemically

▫ Slow stomach poisons – ryania and boric acid▫ Insecticidal soaps, detergents, horticultural oils, and

sucrose octanoate esters Act by suffocation

Other Classifications

• Fungicides and herbicides have similar sets of information, including their resistance groups• Fungicides and herbicides have similar modes of

action to insecticides, but targeting the biochem-istries of fungi and plants▫ The overlap in metabolic pathways is considerable

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Measuring Toxicity to Honey Bees

• Adult worker LD50 (lethal dose 50 percent)▫ Topical▫ Oral • Adult Worker LC50 (lethal concentration)▫ In environment• LD50s and LC50s not usually determined for larval

or pupal honey bees• Impacts of chronic sublethal doses on eventual

adult longevity not determined, either

Considering Synergisms

• Textbook definition of synergism▫ The interaction of things resulting in the overall

effect that is greater than the sum of individual effects of any of them.

• Example of good synergism: mixed pollen diets better for honey bees than any pollen alone

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Considering Synergisms

• Examples of synergisms harmful to honey bees:▫ Fluvalinate and coumaphos (more toxic effects)▫ Fluvalinate and chlorothalonil (more toxic effects)▫ Coumaphos and chlorpyrifos (more toxic effects)▫ Chlorothalonil plus chlorpyrifos, then either fluvalinate

or coumaphos (no observable differences)▫ Imidacloprid and Nosema ceranae Intestinal parasite proliferates

▫ Chlorothalonil and Nosema ceranae Intestinal parasite proliferates

Detoxification of Pesticides

• Basic systems to make pesticides water-soluble for excretion ▫ Oxidation (loss of hydrogen)▫ Reduction (gain of hydrogen)▫ Hydrolysis (reaction with, or addition of water)▫ Hydration (decomposition reaction with water)▫ Dehalogenation (elimination of halides)• Phase I requires cytochrome P450 enzymes

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Cytochrome P450s in Honey Bees

• Fewer types of P450 enzymes in honey bee genome than in mosquitoes or fruit flies• Fewer replicate genes for each P450 enzyme

compared to mosquitoes and fruit flies• Piperonyl butoxide (adjuvant) prevents production

of P450 enzymes• Other, tank-mix agricultural adjuvants just

beginning to get serious attention▫ Toxicity and ability to convey chemicals across

membranes are important considerations

Detoxification of Pesticides

• Phase II requires many functional enzymes to form conjugates that can carry the toxins out of the body:▫ Sulfation; glucoronidation; glutathione conjugation;

acetylation; amino acid conjugation; or methylation• Each of these processes also can be targeted to

disrupt an organism

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Results of Residue Analyses• Multi-year studies on residues (USDA/AMS)▫ Two sources of beehive samples nearly pesticide-free Stored honey and immature bees

▫ Three types of samples very apt to have residues associated with them Stored pollens Beeswax Adult bees

▫ So far, residues of about 150 of the 200 parental and major breakdown products of our agricultural chemicals have been found

Exposure of Honey Bees to Pesticides

• Direct hit▫ Foraging in treated area at time of application▫ Drift over and into the hives• Contact with toxic residues▫ Entering a treated area before toxic residue dries, or

breaks down, on attractive bloom▫ Foraging water over which pesticide has be applied

or into which pesticide has run▫ Consuming contaminated pollen (or nectar) brought

back to the hive before the exposed foragers died

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Avoiding Pesticide Exposure

• Try to choose apiary locations away from pesticide use▫ Hives sometimes can be covered for short periods

when applications are expected: mosquito abatement, agricultural fields, orchards, etc.

▫ Encourage necessary applications be made when pollen and pollen-collecting bees are not going to be contaminated Best advice we can share!

Avoiding Pesticide Exposure

• GET THE WORD OUT!▫ Right now the world is on our side▫ Talk to neighbors, nursery store operators, hardware

store operators, retail store operators, farmers’ market visitors, greens-keepers, PCA’s, Farm Advisors, professional and public service organi-zations that ALL PESTICIDES have demonstrable physiological effects on honey bees if they contact the materials

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Latest Extension Publication on Honey Bee Toxicity• “How to Reduce Bee Poisoning From Pesticides”▫ Pacific Northwest Extension Publication PNW591▫ By L. Hooven, R. Sagili, and E. Johansen▫ Cross-indexed by active ingredient and product name• May be purchased from Washington State or

Oregon State Universities, but is a free web PDF▫ Start with

http://extension.oregonstate.edu/catalog/pdf/pnw/pnw591.pdf

▫ It will take a number of attempts, but just keep entering “PNW 591”and you will find it

Speaker Contacts

• Eric Mussen• Extension Apiculturist• UC Davis• Phone: 530-752-0472• Email: ecmussen@ucdavis.edu• URL: entomology.ucdavis.edu/Faculty/Eric_C_Mussen/