Pesticides: Types and Modes of Action

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Pesticides Types and Modes of Action

• ENY 3225
• or
• ENY 5226

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Learning Objectives

• Learn and internalize definitions
• Be able to list the steps for each mode of action
  for the pesticide groups presented
• Familiarize yourself with the various products
  and which class of insecticide they belong to

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Insecticide

• Any substance or mixture of substances intended
  for preventing, destroying, repelling, or
  mitigating insects.

Often associated with skin irritation
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Vocabulary

• Acetylcholine (ACh). An acetic acid ester of
  choline-a substance that functions as a
  neurotransmitter.
• Acetylcholinesterase. An enzyme in the membrane
  of postsynaptic cells that catalyzes the
  conversion of ACh into choline and acetic acid.
  This enzymatic reaction inactivates the
  neurotransmitter.
• Cholinergic. Denoting nerve endings that
  liberate acetylcholine as a neurotransmitter,
  such as those of the parasympathetic system.
• http//www.mhhe.com/biosci/abio/glossary.mhtml

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Vocabulary

• GABA Gamma-aminobutyric acid believed to
  function as an inhibitory neurotransmitter in the
  central nervous system.
• GABA agonist. Chemical that binds to and
  activates GABA receptors
• GABAergic.
• GABA Antagonists chemicals that bind to but do
  not activate GAMMA-AMINOBUTYRIC ACID receptors,
  thereby blocking the actions of endogenous
  GAMMA-AMINOBUTYRIC ACID or GAMMA-AMINOBUTYRIC
  ACID agonists.
• Suffix -ergic is used to describe the type of
  neurotransmitter a neuron releases

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Vocabulary

• Enzyme. A protein catalyst that increases the
  rate of specific chemical reactions.

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Types of Pesticides

• Insecticide -- kills insects
• Herbicide -- kills weeds
• Fungicide -- kills fungi
• Nematicide -- kills nematodes
• Rodenticide -- kills rodents
• Pisicide -- kills fish

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Other pesticide terms

• Ovicide -- kills eggs
• Larvicide -- kills larvae
• Adulticide -- kill adults
• Insect growth regulator -- disrupts normal growth
  and development of insects
• Dessicants -- cause insect death by dehydration
• Repellents -- repel insects and other arthropods
• Attractants -- attract insects and vertebrates
• Synergists -- chemicals used to enhance the
  insecticidal activity of other chemicals
• piperonyl butoxide
• MGK 264

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Pesticide terms for route of entry

• Stomach poison -- enter orally usually in a food
  material
• Insect baits -- composed of attractive food and a
  toxicant
• Dusts -- applied to surfaces pests contact, pest
  crawls through residue, grooming results in
  ingestion
• Liquid baits -- boric acid and some rodenticides
  are water soluble and can be put in water sources
  of pests

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Pesticide terms for route of entry

• Contact poisons -- enter through cuticle of
  insects
• most pesticides are contact poisons
• most are lipophilic and enter the insect through
  the cuticular waxes and oils
• Fumigants -- vapors enter the insect through the
  spiracles during respiration
• are true gases at room temperature
• methyl bromide, sulfuryl fluoride,
  paradichlorobenzene, napthalene are true fumigants

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Insecticides in UPM

• Inorganics
• Ex. Bora-Care, Disodium Octaborate Tetrahydrate
• Botanicals
• Ex. Pyrethrum
• Synthetic Organics
• Ex. Pyrethroids
• Natural
• Ex. Avermectins

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Modes of Action of Insecticides
Cuticle Production
Endocrine System
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Nervous System

• Lethal spasms and seizures
• Insects flip on back
• Legs wiggle uncontrollably

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Insecticides that Affect the Nervous System
Nervous System
Sodium Channel
DDT
Pyrethroids
permethrin deltamethrin
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Pyrethrins and Pyrethroids

• Pyrethrum -- dust derived from ground
  chrysanthemum flowers
• Pyrethrins -- chemicals within pyrethrum that
  have insecticidal properties

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Pyrethrins and Pyrethroids
Pyrethroids -- synthetically produced chemicals
with similar chemistry and mode of action as
pyrethrins, axonic poisons

• Type I
• Short residual,
• Fast flushing, and
• Quick knockdown,
• Negative temperature correlation more effective
  at low temps
• Ex. Allethrin, d-phenothrin, resemethrin

• Type II
• Long residual,
• Slower flushing, and
• Slower knockdown,
• Better killing power than type 1
• Positive temperature correlation
• Ex. Permethrin, cypermethrin, cyfluthrin,
  lambdacyhalothrin

• Synergists -- used to deactivate mixed function
  oxidases (MFOs) within insects

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Pyrethroids
Permethrin
Deltamethrin
Bifenthrin
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Talstar PL Granular bifenthrin

• Unique sand core granular
• Provides a 2 to 4 month residual, supplying
  effective, long-term protection.
• Penetrates mulch and grass, with no watering
  needed.
• No odor
• Low application rates

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Pyrethroids Effects

• Action on Human System - Irritant
• Systemic Effects - Minimal
• Irritation Effects - Stinging, burning, itching,
  tingling, numbness of skin.

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MOA Pyrethroids

• Axonic poisons
• Bind to a protein called the voltage-gated sodium
  channel
• Normally, the sodium channel opens, causing
  stimulation of the nerve and closes to end the
  nerve signal
• Pyrethroids find to the socium channel and
  prevent it from closing normally
• Result continuous nerve stimulation
• Symptoms Tremors, uncoordinated movement

From Valles and Koehler. 1998. Insecticides
Used in the Urban Environment Mode of Action.
ENY-282
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Nerves and Pyrethroids
Sodium Channels
Direction of Nerve Impulse
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Nervous System

• Why does this happen?
• Lets look at a normal nerve impulse.

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Diagram of a neuron illustrating the subcellular
locations of voltage-gated sodium channels.
5. Presynaptic 7. Postsynaptic
6. Apical dendrites
4. Myelinated
U of Colorado Health Science
3. Unmyelinated
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Axon Membrane at Rest

• Leaky membrane
• K many leaky channels
• Na- few leaky channels
• Outside gtNa-
• Inside gt K

Rensselar Polytechnic Institute
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Axon Membrane

• An action potential is initiated whenever there
  is a stimulus.
• A stimulus is an event that causes depolarization
  or decrease in the membrane potential

Rensselar Polytechnic Institute
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Axon Membrane

• Opening of external Na gates
• Results in influx of Na

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Axon Membrane

• Eventually reach Na equilibrium

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Axon Membrane

• As a result of the depolarization, the internal
  Na gates shut and remain closed for about ½
  millisecond.
• The rapid decrease causes the membrane potential
  to return to the K equilibrium potential.

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Pyrethroid Kill

• Fast action -- 30 minutes to kill
• Excessive nerve firing --spasms

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Pyrethrins and Pyrethroid Labels

• Demon WP
• Demand CS
• Talstar G
• Dragnet
• Deltadust

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Insecticides that Affect the Nervous System
Nervous System
Acetyl- cholinesterase
Sodium Channel
Carbamates Phosphates
DDT
Pyrethroids
permethrin deltamethrin
chlorpyrifos malathion diazinon
propoxur carbaryl
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MOA Carbamates and OPs

• Synaptic poisons
• Carbamates and organophosphorus insecticides bind
  to an enzyme called acetylcholinesterase (AChE)
• AChE is found at the nerve synapse
• AChE is designed to stop a nerve impulse after it
  has crossed the synapse

From Valles and Koehler. 1998. Insecticides
Used in the Urban Environment Mode of Action.
ENY-282
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MOA Carbamates and OPs

• OPs and carbamates bind to AChE
• This prevents AChE from working (i.e., breaking
  down Ach)
• Therefore, nerve impulses continue to fire across
  the synapse
• Symptoms similar to pyrethroid poisoningtremors
  and uncontrolled movement

From Valles and Koehler. 1998. Insecticides
Used in the Urban Environment Mode of Action.
ENY-282
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Cholinesterase Inhibitors

• Organophosphates
• Carbamates

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Organophosphate Effects

• Action on Human System - Inhibits
  acetylcholinesterase enzyme in tissues.
• Systemic Effects - Headache, dizziness, weakness,
  shaking, nausea, stomach cramps, diarrhea,
  sweating.
• Irritation Effects - Minimal rashes, but readily
  absorbed through the skin.
• Delayed/Allergic Effects - Loss of appetite,
  weakness, weight loss, and general feeling of
  sickness. Occasionally permanent harm to brain
  and nervous system.
• Irreversible inhibition of AChE

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N-Methyl Carbamates Effects

• Action on Human System - Reversible changes in
  acetylcholinesterase enzyme in tissues.
• Systemic Effects - Headache, dizziness, weakness,
  shaking, nausea, stomach cramps, diarrhea,
  sweating.
• Irritation Effects - Minimal rashes, but readily
  absorbed through the skin.
• Delayed/Allergic Effects - Loss of appetite,
  weakness, weight loss, and general feeling of
  sickness.
• Reversible inhibition of AChE

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Organophosphates and Carbamates

• Organophosphates
• Chlorpyrifos
• Diazinon
• Trichlorfon
• Parathion
• Carbamates
• Carbaryl (Sevin)
• Propoxur (Baygon)

Chemicals which are derived from phosphoric and
carbamic acid and bond with cholinesterase Acute
toxicity Not persistent Hyper-excitation Insec
t flips on back with legs twitching Sulfur in
formulation often causes strong odor
EPA hit list or not common in UPM
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Organophosphates
Chlorpyrifos ((Dursban)
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Carbamates
Carbaryl (Sevin)
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Dursban Kill

• Vomit and excretion in 8 hours
• Death in 9 hours

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Dursban Chlorpyrifos

• Proven Residual Control
• Effective control makes it the perfect product
  for maintenance accounts.
• Ability to provide control for several weeks,
  keeps customers protected between treatments.
• Broad Label for Varied Applications
• Broad labeling allows use for almost any
  application indoors or out.
• Designed to be used in homes and apartments,
  hospitals, stores, manufacturing plants and
  warehouses.

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Organophosphate and Carbamate Labels

• Dursban Pro
• Dursban TC
• Diazinon G

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Insecticides that Affect the Nervous System
Nervous System
Sodium Channel
Acetyl-cholinesterase
Acetylcholine receptor
Carbamates Phosphates
DDT
Pyrethroids
Neonicotinoids
permethrin deltamethrin
Spinosyns
chlorpyrifos malathion diazinon
imidacloprid thiamethoxam
propoxur carbaryl
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Acetylcholine Receptor

• Mimics acetylcholine on the receptor
• Nicotinic receptor is a type of ACh receptor that
  is sensitive to nicotine
• Cannot be broken down by AChE
• Imidacloprid turns nerve impulse on but AChE does
  not degrade it
• Similar overstimulation as seen with OPs and
  Carbs

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Neonicotinoids

• Imidacloprid (subgroup pyridylmethylamine)
• Advantage pet treatment
• Merit -- turf ornamentals
• Water soluble
• Systemic in plants
• Premise termites
• Affects insects first by paralyzing mouthparts
• Bayer Advantage OTC
• Thiamethoxam (subgroup nitroguanidine)
• Used in crops
• Working on urban and landscape/turf/ornamentals
  label
• (Subgroup nitromethylene)

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Premise Imidacloprid

• No odor
• Not repellent to termites
• Low risk to your family, your pets, your home
• Premise causes a range of effects
• Pests stop feeding
• Premise Plus Nature. This phenomenon makes
  termites susceptible to infection by naturally
  occurring organisms.
• Lateral Soil Movement causes spread to ensure
  thorough soil coverage

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Neonictinoid Labels

• Premise
• Advantage
• Bayer Advantage

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Spinosyns

• Saccharopolyspora spinosa fermetation product
• Soil dwelling
• Success, Naturalyte, Tracer (Dow AgroSciences)
• Testing for UPM

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Insecticides that Affect the Nervous System
Nervous System
Sodium Channel
GABA Receptor
Cholinesterase
Acetylcholine receptor
Carbamates Phosphates
DDT
Pyrethroids
Cyclodienes
Phenyl pyrazoles
Neonicotinoids
permethrin deltamethrin
Spinosyns
chlordane heptachlor
chlorpyrifos malathion diazinon
imidacloprid thiamethoxam
fipronil
propoxur carbaryl
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MOA GABA Antagonist

• Phenylpyrazole (fipronil), cyclodienes
• Antagonists of GABA activated chloride channels
• GABA Antagonists chemicals that bind to but do
  not activate GAMMA-AMINOBUTYRIC ACID receptors,
  thereby blocking the actions of endogenous
  GAMMA-AMINOBUTYRIC ACID or GAMMA-AMINOBUTYRIC
  ACID agonists.
• GABA cant bind to receptor
• Doesnt activate channel (doesnt open)
• Interferes with (prevents) the passage of
  chlorine ions through the channel.
• Concerns with cross resistance with other
  GABAergic insecticides

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GABA Receptor in Central Nervous System

• Phenylpyrazoles or
• Fiproles

GABA
GABA-receptors
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Phenyl pyrazoles

• Fipronil
• Chipco Choice -- mole crickets grubs
• Firestar, Ouver-N-Out, (Ceasefire)--fireants
• Termidor -- termites
• Regent -- corn
• Frontline -- flea tick
• MaxForce FC -- cockroaches and ants

Most lipophilic insecticide ever
discovered Persistent in soil Spread among
social insects on bodies 4 months of residual on
dogs (binds to oils in sebaceous glands)
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MaxForce FC kill

• Loss of muscle control at 17 hours
• Death at about 20 hours

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MaxForce FC Fipronil

• Unique mode of action
• long-term control
• faster results than other ant and cockroach bait
  products
• Fipronil is a highly active, broad-spectrum
  insecticide from the phenyl pyrazole family
• discovered in 1987
• low doses
• highly effective against a broad range of insect
  pests, including ants and roaches

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Phenyl Pyrazole Labels

• MaxForce FC Bait Stations
• Termidor

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Insecticides that Affect the Nervous System
Nervous System
Sodium Channel
GABA Receptor
Cholinesterase
Carbamates Phosphates
Avermectins
DDT
Pyrethroids
Cyclodienes
permethrin deltamethrin
abamectin
Phenylpyrazoles
chlordane heptachlor
chlorpyrifos malathion diazinon
fipronil
propoxur carbaryl
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MOA GABA Agonist

• Avermectins
• Bind to GABA (Gamma-Amino-Butyric Acid gated
  chloride channel
• Opens channel
• Chloride influx
• Cannot reach threshold for action potential
• Causes membrane to hyperpolarize, making it less
  excitatory, decreasing nerve transmission
• Result flaccid paralysis and death

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Avermectins

• Abamectin
• Avert -- cockroaches
• Advance -- ants

Produced from soil microbials. Stomach poison for
ants and cockroaches slow acting low toxicity
to mammals
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Avert Kill

• 22 hours to nerve effects
• 40 hours to kill

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Avert and Advance

• Attractive, long-lasting bait formulations
• Highly effective active ingredient

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Abamectin Labels

• Avert
• Advance
• Raid cockroach bait (class)

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Chlordane kill

• 15 hours to loss of muscle control
• 33 hours to kill

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Modes of Action of Insecticides
Cuticle Production
Endocrine System
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