Associate Certified Entomologist (ACE) Practice Exam

What is the mode of action (MOA) for pyrethroids?

1. Affect potassium channels in nerve axons

2. Affect sodium channels in nerve axons

3. Block calcium channels in muscle cells

4. Inhibit enzyme activity in insect digestion

The correct answer is: Affect sodium channels in nerve axons

Pyrethroids are a class of synthetic insecticides modeled after natural compounds found in chrysanthemum flowers. They primarily exert their insecticidal effects by targeting sodium channels in the nerve cells of insects. When pyrethroids bind to these sodium channels, they cause prolonged opening of the channels, which leads to continuous depolarization of the nerve membrane. This increased excitability results in a disruption of normal nerve function, leading to paralysis and death in the targeted pest. The action on sodium channels is a key characteristic that distinguishes pyrethroids from other classes of insecticides. Understanding this mechanism is vital for effective pest management because it underlines both the efficacy and potential resistance mechanisms pests might develop against such insecticides. This mode of action emphasizes the importance of using integrated pest management strategies to mitigate the development of resistance in pest populations.