Rich Braman
197 lines
14 KiB
Markdown
197 lines
14 KiB
Markdown
# Insecticide Mode of Action — Quick Reference Compendium
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## Extracted from Dr. Michael Scharf's GTBOP Presentation (October 18, 2017)
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**Prepared by:** Rich Braman, UGA Cooperative Extension / Center for Urban Agriculture
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**For:** Dr. Dan Suiter & Dr. Michael Scharf — Bulletin revision reference
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**Source:** GTBOP_ProseTranscript_2017-10-18_InsecticideMOA.md
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---
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## Purpose
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This document consolidates every insecticide class, target site, product name, and relationship mentioned in Dr. Scharf's presentation into reference tables. These can serve as:
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- Quick-check references during the writing process
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- Source material for bulletin tables and figures
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- Verification that all content is accounted for in the revised bulletin
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All content below is derived exclusively from the presentation transcript. Items marked with ⚠️ may benefit from updating with current information.
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---
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## TABLE 1: Master Classification — All Nine Insecticide Classes
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### Neurotoxic Insecticides (5 classes)
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| # | Class | Target Site | Location on Neuron | Mode of Action | Effect on Insect | Representative Products |
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|---|-------|-------------|-------------------|----------------|-----------------|------------------------|
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| 1 | Pyrethroids / Pyrethrins / DDT | Sodium channels | Axon | Stimulation (modulation) | Excitation → knockdown, incoordination | Pyrethroids (various), pyrethrins |
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| 2a | Oxadiazines | Sodium channels | Axon | Blockage | Inhibition → paralysis ("on switch stuck off") | Indoxacarb |
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| 2b | Semicarbazones | Sodium channels | Axon | Blockage | Inhibition → paralysis | Metaflumizone |
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| 3a | Phenylpyrazoles | Chloride channels (GABA receptor) | Post-synaptic | Blockage | Excitation (blocks mellowing effect) | Fipronil |
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| 3b | Isoxazolines | Chloride channels | Post-synaptic | Blockage | Excitation | Fluralaner, sarolaner |
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| 3c | Avermectins | Chloride channels (glutamate receptor) | Post-synaptic | Stimulation | Inhibition → paralysis (opposite of fipronil) | Abamectin |
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| 4a | Neonicotinoids / Nicotinoids | Acetylcholine receptor | Post-synaptic (synapse) | Stimulation | Excitation | Imidacloprid (nicotinoid), clothianidin (neonicotinoid) |
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| 4b | Sulfoximines | Acetylcholine receptor | Post-synaptic (synapse) | Stimulation | Excitation | Sulfoxaflor |
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| 4c | Spinosyns | Acetylcholine receptor | Post-synaptic (synapse) | Stimulation | Excitation | Spinosad |
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| 5 | Organophosphates / Carbamates | Acetylcholinesterase enzyme | Synapse | Inhibition | Excitation (ACh accumulates) | Various ⚠️ |
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### Non-Neurotoxic Insecticides (4 classes)
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| # | Class | Target Site | Mode of Action | Effect on Insect | Representative Products |
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|---|-------|-------------|----------------|-----------------|------------------------|
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| 6 | Diamides | Neuromuscular calcium channels | Stimulation | Contraction → energy depletion → paralysis → death | Chlorantraniliprole, cyantraniliprole |
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| 7a | Juvenile hormone analogs (IGR) | Hormonal regulation of molting | Mimicry | Cuticle deformation, extra juvenile stages, population crash | Pyriproxyfen |
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| 7b | Chitin synthesis inhibitors (IGR) | Chitin synthesis enzyme | Inhibition | Death during molting; "jackknife effect" in termites | Various ⚠️ |
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| 8 | Mitochondrial respiration inhibitors | Mitochondria (respiratory chain) | Inhibition | Energy production failure → death | Hydramethylnon, chlorfenapyr, sulfuryl fluoride, methyl bromide ⚠️, DSOBTH, boric acid |
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| 9 | Cuticle dehydrating dusts | Epicuticular wax layer | Physical abrasion | Water loss → dehydration → death | Silica gel, diatomaceous earth |
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---
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## TABLE 2: Four Basic Modes of Action
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| Mode of Action | What It Does | Example Target | Example Insecticide Class |
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|----------------|-------------|----------------|--------------------------|
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| **Stimulation** | Causes target to become more active | Sodium channels → fire more | Pyrethroids |
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| **Blockage** | Shuts target off | Sodium channels → can't fire | Indoxacarb |
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| **Modulation** | Subtly changes target shape/function | Sodium channel conformation | Pyrethroids (also modulators) |
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| **Inhibition** | Prevents an enzyme from functioning | Acetylcholinesterase → can't degrade ACh | Organophosphates, carbamates |
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*Note: Scharf emphasized that ALL insecticide effects can be categorized into just these four types.*
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---
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## TABLE 3: Target Sites on the Neuron — Spatial Relationships
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| Location | Structure | Natural Function | Insecticides Targeting It |
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|----------|-----------|-----------------|--------------------------|
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| **Axon** (long body of nerve) | Sodium channels | "On switch" — opening initiates nerve impulse | Pyrethroids, pyrethrins, DDT (stimulate); Indoxacarb, metaflumizone (block) |
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| **Post-synaptic membrane** | GABA-gated chloride channels | "Mellowing" — negative chloride dampens activity | Fipronil, isoxazolines (block → excitation) |
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| **Post-synaptic membrane** | Glutamate-gated chloride channels | "Mellowing" — inhibitory | Avermectins/abamectin (stimulate → paralysis) |
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| **Post-synaptic membrane** | Acetylcholine receptors (nAChR) | Carry signal across synapse (sodium channel) | Neonicotinoids, sulfoximines, spinosyns (stimulate) |
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| **Synapse** | Acetylcholinesterase enzyme | Breaks down ACh after signal transmission | Organophosphates, carbamates (inhibit) |
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| **Neuromuscular junction** | Calcium channels | Trigger muscle contraction | Diamides (stimulate → sustained contraction) |
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## TABLE 4: Products and Active Ingredients Mentioned
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| Active Ingredient / Product | Chemical Class | Target Site | Primary Use Mentioned | Notes |
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|----------------------------|---------------|-------------|----------------------|-------|
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| Pyrethrins | Natural pyrethroid | Sodium channels | General knockdown | Rapid knockdown; repellent |
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| Pyrethroids (various) | Synthetic pyrethroids | Sodium channels | General pest control | "Like pepper spray" — highly repellent; widespread bedbug resistance |
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| DDT | Organochlorine | Sodium channels | Historical reference | Same target site as pyrethroids |
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| Indoxacarb | Oxadiazine | Sodium channels (blocker) | Urban pest control | "Really big urban insecticide" |
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| Metaflumizone | Semicarbazone | Sodium channels (blocker) | Ectoparasites; possible urban | Newer product at time of presentation |
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| Fipronil | Phenylpyrazole | Chloride channels (blocker) | Urban pest control | Off-patent; consumer products available; "one of our biggest" |
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| Fluralaner | Isoxazoline | Chloride channels | Veterinary/pet (fleas) | Cross-resistance potential with fipronil |
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| Sarolaner | Isoxazoline | Chloride channels | Veterinary/pet (fleas) | Cross-resistance potential with fipronil |
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| Abamectin | Avermectin | Chloride channels (stimulator) | Gel baits | Opposite effect from fipronil despite similar target |
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| Imidacloprid | Nicotinoid | Acetylcholine receptor | Various | Example of "nicotinoid" (looks more like nicotine) |
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| Clothianidin | Neonicotinoid | Acetylcholine receptor | Various | Example of "neonicotinoid" (structurally evolved from nicotine) |
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| Sulfoxaflor | Sulfoximine | Acetylcholine receptor | Newer product | New class at same target site as neonics |
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| Spinosad | Spinosyn | Acetylcholine receptor | Landscape market | Same target site as neonics |
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| Nicotine | Natural alkaloid | Acetylcholine receptor | Historical (tobacco) | The original — toxic to insects and mammals |
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| Organophosphates (various) | Organophosphate | Acetylcholinesterase | Declining urban use | Not insect-specific; heavy restrictions |
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| Carbamates (various) | Carbamate | Acetylcholinesterase | Declining urban use | Not insect-specific; heavy restrictions |
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| Chlorantraniliprole | Diamide | Calcium channels (muscle) | Various | No signal word required by EPA; manufacturers added "Caution" |
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| Cyantraniliprole | Diamide | Calcium channels (muscle) | Various | Newer diamide |
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| Pyriproxyfen | Juvenile hormone analog | Hormonal (IGR) | Cockroach control | Wing twist indicator in cockroaches |
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| Hydramethylnon | Amidinohydrazone | Mitochondria | Cockroach bait | Energy production inhibitor |
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| Chlorfenapyr | Pyrrole | Mitochondria | Various (has food label) | Relatively safe; resistance potential noted |
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| Sulfuryl fluoride | Inorganic fluoride | Mitochondria | Fumigation | |
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| Methyl bromide | Halogenated hydrocarbon | Mitochondria | Fumigation | ⚠️ Largely phased out |
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| DSOBTH | Borate | Mitochondria/respiration | Wood treatment | Disodium octaborate tetrahydrate |
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| Boric acid | Borate | Mitochondria + gut lining | Various | Dual mode: chemical (respiration) + physical (abrasive/desiccant) |
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| Silica gel | Inorganic dust | Epicuticular wax | Dust application | Physical mode — abrades waxy layer |
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| Diatomaceous earth | Inorganic dust (biogenic) | Epicuticular wax | Dust application | Silicon from ground diatom exoskeletons |
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## TABLE 5: Combination Products
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| Component 1 | Component 2 | Mechanism | Notes |
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|------------|------------|-----------|-------|
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| Neonicotinoid (acetylcholine receptor) | Pyrethroid (sodium channels) | Potentiation — two target sites simultaneously; "1+1=3" synergy | "All start with tea"; dual resistance observed in roach populations; still require rotation |
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## TABLE 6: Insect-Specificity Spectrum
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| Insecticide Class | Mammalian Safety | Notes |
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|-------------------|-----------------|-------|
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| **Diamides** | Extremely high | No signal word required by EPA; 10,000+ x selectivity |
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| **Avermectins** | High | Insect-specific target |
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| **Isoxazolines** | High | Primarily vet/pet products |
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| **IGRs (JH analogs, CSIs)** | High | Target insect-specific developmental processes |
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| **Neonicotinoids** | Moderate-High | Insect-specific receptor but systemic/pollinator concerns |
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| **Fipronil** | Moderate-High | GABA receptor differences provide selectivity |
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| **Pyrethroids** | Moderate | Generally safe for mammals but repellent to insects |
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| **Organophosphates / Carbamates** | **Low** | **Not insect-specific; work against mammals equally** |
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*Spectrum based on Scharf's characterizations in the presentation. Not a quantitative ranking.*
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## TABLE 7: Practical Field Indicators Mentioned
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| What You See | What It Means | Relevant Product/Class |
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|-------------|--------------|----------------------|
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| Immediate knockdown/incoordination | Sodium channel excitation | Pyrethroids, pyrethrins |
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| Paralysis (insect immobile but alive) | Sodium channel blockage OR chloride stimulation | Indoxacarb, abamectin |
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| Wing twist in cockroach nymphs/adults | Juvenile hormone disruption | Pyriproxyfen (JH analog IGR) |
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| "Jackknife" body curl in termites | Malformed cuticle from chitin synthesis disruption | Chitin synthesis inhibitors |
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| Lethargy and desiccation | Epicuticular wax loss | Silica gel, diatomaceous earth |
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| Sustained muscle contraction → stillness | Calcium channel stimulation → energy depletion | Diamides (chlorantraniliprole, cyantraniliprole) |
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## TABLE 8: Key Physiological Barriers to Insecticide Penetration
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| Barrier | Location | Challenge for Insecticide | Relevant Formulation Strategy |
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|---------|----------|--------------------------|------------------------------|
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| Cuticle | External body surface | Multi-layered; waterproof; waxy epicuticle | Contact formulations must penetrate all layers |
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| Gut lining | Digestive tract interior | The "tube" inside is technically external to the body | Baits must cross gut wall to reach internal targets |
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| Tracheal system | Throughout body | Physical tubes, not blood-carried oxygen | Fumigants exploit this unique insect anatomy |
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## TABLE 9: Key Terminology and Definitions from Presentation
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| Term | Definition (as explained by Scharf) |
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|------|--------------------------------------|
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| **LD50** | Lethal dose that kills 50% of test population; inverse relationship with toxicity (lower LD50 = more toxic) |
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| **Mode of action** | The action of an insecticide at its target site (stimulation, blockage, modulation, or inhibition) |
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| **Target site** | The specific protein or physiological location within the insect where an insecticide acts |
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| **Signal word** | EPA-required label indicator of acute toxicity (Danger, Warning, Caution); diamides so safe none was required |
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| **Potentiation** | Synergistic effect from hitting two target sites simultaneously; "one plus one equals three" |
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| **Trophallaxis** | Food sharing among social insects (from mouth and anus); insecticide transfer mechanism |
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| **Allogrooming** | Mutual grooming among social insects; insecticide transfer mechanism |
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| **Secondary kill** | Death of an individual from consuming insecticide-contaminated feces or carcass of a treated individual |
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| **Tertiary kill** | Death of a third individual from insecticide passed through two prior digestive tracts |
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| **IRAC** | Insecticide Resistance Action Committee; industry body that classifies MOAs and publishes rotation guidance |
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| **Wing twist** | Visible cuticle deformation in cockroaches exposed to juvenile hormone analog IGRs; field diagnostic indicator |
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| **Jackknife effect** | Body curling in termites with malformed cuticle from chitin synthesis inhibitor exposure |
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| **Epicuticle** | Outermost waxy/oily layer of insect cuticle; target of dehydrating dusts |
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| **Synapse** | Gap between neurons where electrical signals convert to chemical (neurotransmitter) signals |
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| **Acetylcholine** | Primary neurotransmitter that crosses synapses in the insect nervous system |
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| **GABA receptor** | Chloride channel type at post-synaptic membrane; target of fipronil |
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| **Glutamate receptor** | Chloride channel type; target of avermectins |
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## Cross-Reference: Same Target Site, Different Effects
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One of the presentation's key teaching points was that different insecticide classes can target the same site but have opposite effects:
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| Target Site | Insecticide A | Effect A | Insecticide B | Effect B |
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|------------|--------------|---------|--------------|---------|
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| Sodium channels | Pyrethroids | Stimulation → excitation | Indoxacarb | Blockage → paralysis |
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| Chloride channels | Fipronil | Blockage → excitation | Abamectin | Stimulation → paralysis |
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*This contrast is valuable for teaching and for resistance management — switching between classes at the same site may still provide different selection pressures.*
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*All data extracted exclusively from the October 18, 2017 GTBOP presentation by Dr. Michael Scharf as transcribed and corrected through the GTBOP archive pipeline. Items marked ⚠️ may have changed since the presentation date.*
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