Summary of Insecticide Classification and Modes of Action

Module Overview

  • Focus on classification of insecticides, characteristics, and modes of action (MoA).

Targets of Insecticides

  • Insecticides target various physiological processes in insects.

Mode of Action (MoA) Classification

  • Key to resistance management.

  • Each group has specific mechanism affecting insect physiology.

Group 1: Acetylcholinesterase (AChE) Inhibitors

  • Carbamates:

    • Derived from carbamic acid.

    • Inhibit AChE, causing hyperexcitation.

    • Reversible and less toxic compared to organophosphates (OP).

  • Organophosphates:

    • Developed during WWII; highly toxic; irreversible binding to AChE.

    • Used for rapid control but with environmental concerns.

Group 2: GABA-gated Chloride Channel Blockers

  • Block GABA-activated chloride channels, leading to hyperexcitation and convulsions.

  • Example: Endosulfan, banned in some regions for toxicity and environmental persistence.

Group 3: Sodium Channel Modulators

  • Keep sodium channels open; leads to hyperexcitation and potential nerve blockage.

  • Examples: Pyrethroids

    • Developed in the 1960s; highly effective at low doses.

    • DDT: First synthesized in 1874; effective in controlling diseases.

Group 4: Nicotinic Acetylcholine Receptor (nAChR) Modulators

  • Compounds either competitively or allosterically modulate nAChRs, causing paralysis or hyper-excitation.

  • Neonicotinoids: Effective against various pests but controversial regarding bee population impacts.

Group 5: Allosteric Modulators of nAChR

  • Spinosyns: Derived from bacteria, low toxicity to mammals but toxic to beneficial insects.

Group 6: Glutamate-gated Chloride Channel Modulators

  • Activate GluCls leading to paralysis.

Group 7: Juvenile Hormone Mimics

  • Disrupts and prevents metamorphosis, leading to abnormal growth and reproduction.

Group 11: Microbial Disruptors of Insect Midgut Membranes

  • Bacillus thuringiensis (Bt): Produces crystal proteins toxic to larvae.

Group 14: nAChR Channel Blockers

  • Block nAChRs leading to paralysis; Nereistoxin is a key example.

Group 15/16: Chitin Biosynthesis Inhibitors

  • Disrupt chitin formation, affecting insect growth and molting.

Group 18: Ecdysone Receptor Agonists

  • Mimic molting hormones.

Group 28: Ryanodine Receptor Modulators

  • Induces muscle contraction leading to paralysis.

Group 31: Baculoviruses

  • Naturally infect insects, causing death and facilitating further viral spread.

Fungal Agents (Unknown MoA)

  • Biological control agents that primarily affect specific pest species with low non-target impacts.

Summary

  • Knowledge of insecticide modes of action is crucial for effective pest management and understanding potential environmental impacts.