Question

What is the mode of action of neonicotinoid insecticides?

• A. Inhibits Acetyl cholinesterase
• B. Binds with Nicotinic acetyl choline receptors
• C. Blocks voltage-gated sodium channel
• D. Blocks Chloride channel

Hint:

Neonicotinoids act as post-synaptic agonists at the nAChR (Group 4), mimicking acetylcholine but resisting degradation by acetylcholinesterase.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Insecticides are classified into distinct groups based on their specific physiological mode of action within the insect's nervous or metabolic systems.
Neonicotinoids are a widely used class of systemic insecticides with excellent efficacy against sucking pests.

Step 2: Detailed Explanation:
Neonicotinoids (such as Imidacloprid, Thiamethoxam, Acetamiprid, and Clothianidin) are classified under the IRAC system as Group 4: Nicotinic acetylcholine receptor (nAChR) agonists.
These compounds mimic the natural neurotransmitter acetylcholine (ACh).
They bind systemically and irreversibly to the post-synaptic nicotinic acetylcholine receptors in the insect's central nervous system.
Unlike natural acetylcholine, neonicotinoid molecules cannot be broken down by the enzyme acetylcholinesterase (AChE).
This persistent binding leads to continuous, uncontrolled nerve firing, causing hyperexcitation, convulsions, paralysis, and ultimately death.
Let us review the modes of action of the other choices:
1. Inhibits Acetylcholinesterase: E.g., Organophosphates and Carbamates.
2. Blocks voltage-gated sodium channels: E.g., Indoxacarb, Metaflumizone.
3. Blocks GABA-gated chloride channels: E.g., Fipronil (phenylpyrazoles) and Cyclodienes.

Step 3: Final Answer:
Therefore, the mode of action of neonicotinoids is that they bind with Nicotinic acetylcholine receptors.