Principles of Insecticide Mode of Action | Dr. Michael Scharf | GTBOP Structural Pest Control Webinar Series
Dr. Michael Scharf of Purdue University presents a comprehensive overview of insecticide classification and mode of action for pest management professionals. Scharf covers insect physiology fundamentals, the key-and-lock relationship between insecticides and target sites, and nine insecticide classifications — five neurotoxic and four non-neurotoxic. The presentation concludes with practical factors affecting performance including formulations, pest behavior, sanitation, and resistance management. Q&A moderated by Dr. Dan Suiter.
Presented: October 18, 2017 Series: Getting the Best of Pests — Structural Pest Control Webinar Series Host: UGA Center for Urban Agriculture CEU Credits: GA — 2 HPC (Cat 35)
TIMESTAMPS 0:00 Introduction and Speaker Credentials 1:45 Why Understanding Mode of Action Matters 6:03 Presentation Outline 7:13 Additional Resources — PCT Article and UGA Publication 8:26 Insect Physiology Overview — Nervous System, Cuticle, Gut, Trachea, Muscles 14:02 Insecticide Classification Basics — Chemical Structure 16:01 Target Site and Mode of Action — Key and Lock Analogy 17:51 Four Basic Modes of Action — Stimulation, Blockage, Modulation, Inhibition 19:41 The LD50 Concept and Mammalian Safety 22:46 Overview of Neurotoxic and Non-Neurotoxic Classifications 23:36 The Insect Nervous System — Neurons, Synapses, Neurotransmitters 26:45 Neurophysiology Demonstration — Fipronil and Nerve Excitation 28:40 Nervous System Target Sites — Roadmap of Ion Channels and Receptors 32:24 Sodium Channel Insecticides — Pyrethroids, Indoxacarb, Metaflumizone 34:12 Chloride Channel Insecticides — Fipronil, Isoxazolines, Abamectin 36:20 Acetylcholine Receptor Insecticides — Nicotinoids, Sulfoximines, Spinosyns 37:28 Acetylcholinesterase Inhibitors — Organophosphates and Carbamates 38:04 Combination Products — Nicotinoid-Pyrethroid Potentiation 39:07 Non-Neurotoxic Insecticides Overview 40:02 Muscular Calcium Channel Agents — Diamides 41:42 Insect Growth Regulators — JH Analogs and Chitin Synthesis Inhibitors 45:18 Inhibitors of Energy Production — Hydramethylnon, Chlorfenapyr, Fumigants 46:56 Cuticle Dehydrating Dusts — Silica Gel and Diatomaceous Earth 48:15 Factors Affecting Insecticide Efficacy 48:46 Stability, Persistence, and Formulations 51:02 Pest Behavior — Secondary and Tertiary Kill, Trophallaxis 53:04 Sanitation and IPM 54:19 Resistance Management — Rotation Strategies 56:30 Summary Points 57:44 Additional Resources 57:53 Q&A — Combination Product Resistance 59:53 Q&A — Flow of New Active Ingredients to Market 1:01:08 Q&A — Chlorantraniliprole and Non-Target Invertebrates 1:01:40 Q&A — IRAC Classification System 1:02:38 Q&A — Nicotinoids vs. Neonicotinoids 1:03:43 Q&A — Oral vs. Dermal Toxicity Routes 1:04:43 Q&A — Repellent vs. Non-Repellent Insecticides 1:05:32 Q&A — Essential Oils and 25B Exempt Products
FREQUENTLY ASKED QUESTIONS
Q: What are the four basic insecticide modes of action? A: All insecticides disrupt target sites through stimulation, blockage, modulation, or inhibition. Understanding these four mechanisms provides a framework for classifying any product a professional might encounter.
Q: Why are diamide insecticides considered especially safe for mammals? A: Diamides target insect-specific muscular calcium channels. Their mammalian toxicity is so low that the EPA initially required no signal word, though manufacturers voluntarily adopted a "caution" label.
Q: Why is resistance a major concern in cockroach management? A: Research has documented cockroaches surviving on bait as their sole food source for a month. Even combination products face dual resistance. Rotate active ingredients every three months or monthly.
Q: How does the IRAC help pest management professionals? A: The Insecticide Resistance Action Committee classifies active ingredients by mode of action, helping professionals plan rotations between different target site groups rather than simply switching trade names.
Q: What is the difference between repellent and non-repellent insecticides? A: The distinction largely comes down to pyrethroids versus everything else. Pyrethroids are highly detectable to insects — like "pepper spray" — while most other actives are not nearly as detectable.
RESOURCES • Scharf & Suiter, "Insecticide Primer and Insecticide Mode of Action," PCT Magazine, 2011 • Scharf & Suiter, "Insecticide Basics for the Pest Management Professional," UGA publication • IRAC Mode of Action Classification Chart: https://irac-online.org