Pesticides: Types and Modes of Action

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. • http://www.mhhe.com/biosci/abio/glossary.mhtml

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

12. Nervous System Energy Production Water Balance Modes of Action of Insecticides 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 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. 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 Pyrethrins and Pyrethroids 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

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. 1998. Insecticides Used in the Urban Environment: Mode of Action. ENY-282

21. Repeated nerve firing Nerves and Pyrethroids 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 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. 1998. 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. 1998. Insecticides Used in the Urban Environment: Mode of Action. ENY-282

34. Causes repeated nerve firing Cholinesterase Inhibitors • Organophosphates • Carbamates

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 • 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 Insect flips on back with legs twitching Sulfur in formulation often causes strong odor *EPA hit list or not common in UPM

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

40. O CH3 -- N -- C O -- H Carbamic Acid O CH3 -- N -- C O -- R Carbamate Carbamates 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 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 Nervous System Sodium Channel GABA Receptor Cholinesterase Acetylcholine receptor Carbamates Phosphates DDT Pyrethroids Phenyl pyrazoles Cyclodienes Neonicotinoids permethrin deltamethrin Spinosyns chlordane heptachlor chlorpyrifos malathion diazinon imidacloprid thiamethoxam fipronil propoxur carbaryl