1. Pesticides: Types and Modes of Action
ENY 3225 or
ENY 5226

2. 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

3. Insecticide
Any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating insects.
Often associated
with skin irritation

4. 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.

5. 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

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

7. Types of Pesticides Insecticide -- kills insects
Herbicide -- kills weeds
Fungicide -- kills fungi
Nematicide -- kills nematodes
Rodenticide -- kills rodents
Pisicide -- kills fish

8. 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

9. 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

10. 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

11. Insecticides in UPM Inorganics Botanicals Synthetic Organics “Natural”
Ex. Bora-Care, Disodium Octaborate Tetrahydrate
Botanicals
Ex. Pyrethrum
Synthetic Organics
Ex. Pyrethroids
“Natural”
Ex. Avermectins

12. Modes of Action of Insecticides
Nervous System
Water Balance
Energy Production
Cuticle Production
Endocrine System

13. Nervous System Lethal spasms and seizures Insects flip on back
Legs wiggle uncontrollably

14. Insecticides that Affect the Nervous System
Sodium Channel
DDT
Pyrethroids
permethrin
deltamethrin

15. Pyrethrins and Pyrethroids
Pyrethrum -- dust derived from ground chrysanthemum flowers
Pyrethrins -- chemicals within pyrethrum that have insecticidal properties

16. 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

17. Pyrethroids
Permethrin
Deltamethrin
Bifenthrin

18. 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

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

20. 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 Insecticides Used in the Urban Environment: Mode of Action. ENY-282

21. Nerves and Pyrethroids
Repeated nerve firing
Sodium Channels
Direction of Nerve Impulse

22. Nervous System Why does this happen?
Let’s look at a “normal” nerve impulse.

23. “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

24. Axon Membrane at Rest “Leaky membrane” K+: many leaky channels
Na-: few leaky channels
Outside: >Na-
Inside: > K+
Rensselar Polytechnic Institute

25. 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

26. Axon Membrane
Opening of external Na gates
Results in influx of Na

27. Axon Membrane
Eventually reach Na equilibrium

28. 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.

29. Pyrethroid Kill Fast action -- 30 minutes to kill
Excessive nerve firing --spasms

30. Pyrethrins and Pyrethroid Labels
Demon WP
Demand CS
Talstar G
Dragnet
Deltadust

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

32. 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 Insecticides Used in the Urban Environment: Mode of Action. ENY-282

33. 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 Insecticides Used in the Urban Environment: Mode of Action. ENY-282

34. Cholinesterase Inhibitors
Organophosphates
Carbamates
Causes repeated nerve firing

36. 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

37. 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

38. Organophosphates and Carbamates
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
Insect flips on back with legs twitching
Sulfur in formulation often causes strong odor
*EPA hit list or not common in UPM

39. Organophosphates O -- H H -- O -- P Phosphoric Acid O O -- R’
R -- O -- P O
O -- R’
S -- R”
Phosphorothioate
H -- O -- P
O -- H
Phosphoric Acid
Chlorpyrifos ((Dursban)

40. Carbamates O CH3 -- N -- C O -- H Carbamic Acid O -- R
Carbaryl (Sevin)

41. Dursban Kill
Vomit and excretion in 8 hours
Death in 9 hours

42. 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.

43. Organophosphate and Carbamate Labels
Dursban Pro
Dursban TC
Diazinon G

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

45. 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

46. 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)

47. 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

48. Neonictinoid Labels
Premise
Advantage
Bayer Advantage

49. Spinosyns Saccharopolyspora spinosa fermetation product Soil dwelling
Success*, Naturalyte*, Tracer* (Dow AgroSciences)
Testing for UPM

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

51. 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

52. GABA Receptor in Central Nervous System
Phenylpyrazoles or
Fiproles
GABA
GABA receptor
Chloride ions
Fipronil
GABA
GABA-receptors

53. Phenyl pyrazoles Most lipophilic insecticide ever discovered
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)

54. MaxForce FC kill Loss of muscle control at 17 hours
Death at about 20 hours

55. 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

56. Phenyl Pyrazole Labels
MaxForce FC Bait Stations
Termidor

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

58. 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

59. Avermectins Abamectin Avert -- cockroaches Advance -- ants
Produced from soil microbials. Stomach poison for ants and cockroaches
slow acting
low toxicity to mammals

60. Avert Kill
22 hours to nerve effects
40 hours to kill

61. Avert and Advance Attractive, long-lasting bait formulations
Highly effective active ingredient

62. Abamectin Labels
Avert
Advance
Raid cockroach bait (class)

63. Chlordane kill
15 hours to loss of muscle control
33 hours to kill

64. Modes of Action of Insecticides
Nervous System
Water Balance
Energy Production
Cuticle Production
Endocrine System