Why are organophosphates toxic to insects?

• A. They inhibit photosynthesis.
• B. They inhibit the enzyme acetylcholinesterase, which is essential for nerve function.
• C. They disrupt the insect cuticle.
• D. They block potassium channels.

Answer: (B)

Organophosphates are toxic to insects because they inhibit acetylcholinesterase, the enzyme that normally breaks down acetylcholine at nerve synapses. When acetylcholinesterase is blocked, acetylcholine accumulates in the synaptic cleft, causing continuous stimulation of nerve and muscle receptors. This leads to overstimulation of nerves, uncoordinated movement, convulsions, paralysis, and ultimately death. Organophosphates form a covalent bond with the enzyme’s active site, creating a lasting inhibition that can be difficult to reverse; antidotes can help if given early, but aging of the bond makes reactivation harder over time. The other options don’t describe how organophosphates disrupt nervous signaling—photosynthesis inhibition relates to herbicides, cuticle disruption is a physical barrier effect, and potassium-channel blockade refers to different ion-channel mechanisms.