Jennifer Gervais, Ph.D.

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Review of Insecticide Classes and Their Toxicity
October 8, 2008 Western Horticultural Inspection
Society

• Jennifer Gervais, Ph.D.
• Pesticide Specialist
• National Pesticide Information Center

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Pesticide Toxicity

• Risk Toxicity Exposure

• Toxicity is influenced by

Active Ingredient
Concentration
Formulation
Other ingredients
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Pesticide Toxicity
Toxicity Classes and Signal Words
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Exposure

• Three Main Routes

Dermal
Inhalation
Oral

• Steps can be taken to reduce exposure

Personal Protective Equipment
Re-entry intervals
Pre-harvest intervals
Tolerances
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Environmental Hazards
Specified on label
Toxicity triggers label language
Label Review Manual

• Soil, water, air, beneficial insects,
• fish and wildlife, plants

• 7 acute toxicity studies required

• Environmental fate information

• Pattern of use, or history of incidents
• also considered

Manual http//www.epa.gov/oppfead1/labeling/lrm
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Pesticide Classes
Organophosphates/carbamates
Pyrethrins/pyrethroids
Organochlorines
Neonicotinoids
Bacterial products
Others
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Organophosphates/Carbamates
Example pesticides
OP
Carbamate
Sevin (carbaryl)
Orthene (acephate)
Malathion (malathion)
Imidan 70W (phosmet)
Cygon (dimethoate)
Lorsban 4E (chlorpyrifos)
Metasystox-R (oxydemeton-methyl)
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Organophosphates/Carbamates

• Similar mechanism of toxicity

• Bind to acetylcholinesterase in
• nerve synapses

• Off switch deactivated- continuous
• firing

• Binding affinity varies, but
• carbamate binding reversible

• Additive toxicity possible

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Mode of Action
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Toxicity
Carbamates

• Slightly to highly toxic to birds

• Moderately to highly toxic to fish

• Highly toxic to bees

Organophosphates

• Most are highly toxic to birds

• Moderately to highly toxic to fish

• Moderately to highly toxic to bees

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Pyrethroids
Example pesticides
Talstar (bifenthrin)
Scimitar (lambda cyhalothrin)
Tame (fenopathrin)
Tempo (cyfluthrin)
Over 20 pyrethroid active ingredients
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Pyrethroids
Pyrethrum extract of chrysanthemums
Pyrethrins refined extracts

• Frequently used with synergists
• such as MGK-264 and
• piperonyl butoxide

• Break down rapidly in environment

Pyrethroids synthetic derivatives
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Pyrethroids
Classified into types I and II Chemical
structure and effects Environmental persistence
Pyrethroids bind to sodium ion channel in nerve
cell membrane
Prevent channel closure
Type II may also interfere with
neuro- transmitter (GABA) function
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Pyrethroid Toxicity
Most not well absorbed across skin or through
lungs
Rapidly metabolized and excreted by mammalian
liver and kidneys
Greater toxicity to insects due to greater
sensitivity of ion channels lower body
temperature slower biotransformation
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Pyrethroid Toxicity

• Pyrethroids highly toxic to bees,
• fish, and aquatic invertebrates

• Pyrethroid impacts to aquatic systems
• may be great
• CA studies
• CA DPR, EPA reviews

• Unexpected environmental
• behavior

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Organochlorines

• Largely phased out in the US
• highly environmentally persistent
• potential for bioaccumulation
• sublethal effects

• Example pesticide
• Thiodan (endosulfan)

• Disrupt sodium/potassium ion balance
• causing constant signal transmission

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Endosulfan

• Highly toxic to mammals

• Does not bioaccumulate

• Moderately to highly toxic to birds

• Highly toxic to fish, aquatic inverts

• Moderate toxicity to bees, beneficials

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Neonicotinoids

• Chemically related to nicotine

• Activate nicotinic acetylcholine receptors

• Prolonged depolarization and receptor
• paralysis

• nACh receptors vary within and among
• species

• Receptor specificity of neonicotinoids
• varies

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Neonicotinoids
Example pesticides Merit (imidacloprid) Maratho
n (imidacloprid)
Clothianidin Factor in CCD? Now banned in some
countries Registered products in Oregon
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Neonicotinoid Toxicity
Imidacloprid and Clothianidin

• Moderate toxicity to mammals

• Highly variable toxicity to birds

• Highly toxic to some aquatic
• invertebrates but not others

• Low toxicity to fish

• Highly toxic to bees

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Bacterial Products
Example pesticides Avid (abamectin) mix of
avermectins Conserve SC (spinosad)
Fermentation products of actinomycete bacteria
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Bacterial Products
Avermectins- Abamectin

• Activate chloride channels gated by
• GABA neurotransmitter receptors

• High acute toxicity to mammals, highly
• variable in birds

• Highly toxic to fish, bees, aquatic inverts

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Bacterial Products
Spinosyns- Spinosad

• Activates nicotinic acetylcholine receptors

• Unique mode of action/site, mechanism not yet
• well understood

• Affects GABA receptor function

• Slightly to moderately toxic to mammals

• Practically nontoxic to slightly toxic to birds

• Moderately to very highly toxic to fish and
• aquatic invertebrates, highly toxic to bees

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Miscellaneous
Azadirachtin

• Example pesticide Azatin

• Extract of Neem tree seeds

• Structurally similar to
• ecdysone hormones in insects

• Blocks insect molt, also deters feeding

• Low toxicity to birds, mammals, fish,
• beneficials (must be eaten)

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Miscellaneous
Diflubenzuron

• Example pesticide Dimilin

• Benzoylphenylurea

• Interferes with chitin synthesis (inhibit
• chitin synthetase)

• Egg hatch, larval secretion of
• chitin, juvenile molt affected

• Low acute nontarget toxicity

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Miscellaneous
Pymetrozine

• Example pesticide Endeavor

• Pyridine azomethine- not used
• previously as an insecticide

• Blocks feeding of Homopteran insects

Stylus unable to penetrate plant Neuroregulaton
or nerve-muscle effect?

• Category III, IV acute toxicity

• Low toxicity to birds, fish, bees

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National Pesticide Information Center
Answers pesticide-related inquiries by telephone
7 days a week
Website resources include

• Active ingredient fact sheets

• Databases on environmental fate
• and health effects

• Portal to label databases

Hours 630 430 PST 7 days a week
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NATIONAL PESTICIDE INFORMATION CENTER
1-800-858-7378 (1-800-858-PEST)
http//npic.orst.edu
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Questions?