pesticides: types and modes of action eny 3225 or eny 5226
TRANSCRIPT
Pesticides: Types and Modes of Action
ENY 3225or
ENY 5226
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
Insecticide
• Any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating insects.
Often associated with skin irritation
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
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
Vocabulary
• Enzyme. A protein catalyst that increases the rate of specific chemical reactions.
Types of Pesticides
• Insecticide -- kills insects• Herbicide -- kills weeds• Fungicide -- kills fungi• Nematicide -- kills nematodes• Rodenticide -- kills rodents• Pisicide -- kills fish
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
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
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
Insecticides in UPM
• Inorganics– Ex. Bora-Care, Disodium Octaborate
Tetrahydrate
• Botanicals– Ex. Pyrethrum
• Synthetic Organics– Ex. Pyrethroids
• “Natural”– Ex. Avermectins
Modes of Action of Insecticides
Nervous System Energy Production
Cuticle Production
Water Balance
Endocrine System
Nervous System
• Lethal spasms and seizures• Insects flip on back• Legs wiggle uncontrollably
Insecticides that Affect the Nervous System
Nervous System
permethrindeltamethrin
PyrethroidsDDT
Sodium Channel
Pyrethrins and Pyrethroids
• Pyrethrum -- dust derived from ground chrysanthemum flowers
• Pyrethrins -- chemicals within pyrethrum that have insecticidal properties
Pyrethrins and Pyrethroids
• 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
Pyrethroids -- synthetically produced chemicals with similar chemistry and mode of action as pyrethrins, axonic poisons
•Synergists -- used to deactivate mixed function oxidases (MFOs) within insects
Pyrethroids
Permethrin
Bifenthrin Deltamethrin
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
Pyrethroids Effects
• Action on Human System - Irritant
• Systemic Effects - Minimal
• Irritation Effects - Stinging, burning, itching, tingling, numbness of skin.
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
Nerves and Pyrethroids
Sodium Channels
Direction of Nerve Impulse Repeated nerve firing
Nervous System
• Why does this happen?• Let’s look at a “normal” nerve
impulse.
“Diagram of a neuron illustrating the subcellular locations of voltage-gated sodium channels.”
#4. Myelinated#4. Myelinated
#3. Unmyelinated#3. Unmyelinated
#6. Apical dendrites#6. Apical dendrites
#5. Presynaptic#5. Presynaptic#7. Postsynaptic#7. Postsynaptic
U of ColoradoHealth Science
Rensselar Polytechnic Institute
Axon Membrane at Rest
1. “Leaky membrane”K+: many leaky
channelsNa-: few leaky
channels2. Outside: >Na-3. Inside: > K+
Axon Membrane
Rensselar Polytechnic Institute
1. An action potential is initiated whenever there is a stimulus.
2. A stimulus is an event that causes depolarization or decrease in the membrane potential
Axon Membrane
1. Opening of external Na gates
2. Results in influx of Na
Axon Membrane1. Eventually reach
Na equilibrium
Axon Membrane1. As a result of the
depolarization, the internal Na+ gates shut and remain closed for about ½ millisecond.
2. The rapid decrease causes the membrane potential to return to the K equilibrium potential.
Pyrethroid Kill• Fast action -- 30 minutes to kill• Excessive nerve firing --spasms
Pyrethrins and Pyrethroid Labels
• Demon WP• Demand CS• Talstar G• Dragnet• Deltadust
Acetyl-cholinesterase
Insecticides that Affect the
Nervous System Nervous System
propoxurcarbaryl
permethrindeltamethrin
PyrethroidsDDT
Sodium Channel
CarbamatesPhosphates
chlorpyrifosmalathiondiazinon
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
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
poisoning—tremors and uncontrolled movement
From Valles and Koehler. 1998. Insecticides Used in the Urban Environment: Mode of Action. ENY-282
Cholinesterase Inhibitors
• Organophosphates• Carbamates
Causes repeated nerve firing
Acetylcholine SystemAcetylcholine System
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
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
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 toxicityNot persistentHyper-excitationInsect flips on back with legs twitchingSulfur in formulation often causes strong odor
*EPA hit list or not common in UPM
Organophosphates
R -- O -- P
OO -- R’
S -- R”Phosphorothioate
H -- O -- P
OO -- H
O -- H
Phosphoric Acid
Chlorpyrifos ((Dursban)
Carbamates
Carbamate
CH3 -- N -- C
O
O -- HCarbamic Acid
CH3 -- N -- C
O
O -- RCarbaryl (Sevin)
Dursban Kill• Vomit and excretion in 8 hours• Death in 9 hours
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.
Organophosphate and Carbamate Labels
• Dursban Pro• Dursban TC• Diazinon G
Insecticides that Affect the
Nervous System Nervous System
propoxurcarbaryl
permethrindeltamethrin
PyrethroidsDDT
Sodium Channel
CarbamatesPhosphates
Neonicotinoids
Acetylcholine receptor
Acetyl-cholinesterase
chlorpyrifosmalathiondiazinon
Spinosyns
imidaclopridthiamethoxam
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
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)
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
Neonictinoid Labels
• Premise• Advantage• Bayer Advantage
Spinosyns
• Saccharopolyspora spinosa fermetation product
• Soil dwelling• Success*, Naturalyte*, Tracer*
(Dow AgroSciences)• Testing for UPM
Insecticides that Affect the Nervous System
Nervous System
propoxurcarbaryl
permethrindeltamethrin
PyrethroidsDDT
Sodium Channel
chlordaneheptachlor
Cyclodienes
fipronil
Phenyl pyrazoles
GABA Receptor
CarbamatesPhosphates
Cholinesterase
chlorpyrifosmalathiondiazinon
Neonicotinoids
Acetylcholine receptor
Spinosyns
imidaclopridthiamethoxam
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 can’t bind to receptor• Doesn’t activate channel (doesn’t open)• Interferes with (prevents) the passage of chlorine
ions through the channel.• Concerns with cross resistance with other
GABAergic insecticides
GABA
GABA receptor
GABA Receptor in Central Nervous
System• Phenylpyrazoles or• Fiproles
GABA-receptors
GABAChloride ions
Fipronil
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 soilSpread among social insects on
bodies4 months of residual on dogs (binds
to oils in sebaceous glands)
MaxForce FC kill• Loss of muscle control at 17 hours• Death at about 20 hours
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
Phenyl Pyrazole Labels
• MaxForce FC Bait Stations • Termidor
Insecticides that Affect the
Nervous System Nervous System
propoxurcarbaryl
permethrindeltamethrin
PyrethroidsDDT
Sodium Channel
abamectin
Avermectins
chlordaneheptachlor
Cyclodienes
fipronil
Phenylpyrazoles
GABA Receptor
CarbamatesPhosphates
Cholinesterase
chlorpyrifosmalathiondiazinon
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
Avermectins
• Abamectin– Avert --
cockroaches– Advance -- ants
Produced from soil microbials. Stomach poison for ants and cockroaches
slow actinglow toxicity to mammals
Avert Kill• 22 hours to nerve effects• 40 hours to kill
Avert and Advance
• Attractive, long-lasting bait formulations
• Highly effective active ingredient
Abamectin Labels
• Avert• Advance• Raid
cockroach bait (class)
Chlordane kill• 15 hours to loss of muscle control• 33 hours to kill
Modes of Action of Insecticides
Nervous System Energy Production
Cuticle Production
Water Balance
Endocrine System