To which IRAC sub-group do organophosphate insecticides like Acephate and Phosmet belong?

• A. 2A, carbamate acetylcholinesterase inhibitors
• B. 3B, pyrethroid sodium channel modulators
• C. 1B, organophosphate acetylcholinesterase (AChE) inhibitors
• D. 4C, juvenile hormone disruptors

Answer: (C)

Organophosphate insecticides such as Acephate and Phosmet act by inhibiting acetylcholinesterase, the enzyme that normally breaks down acetylcholine at insect nerve synapses. When AChE is blocked, acetylcholine accumulates, causing continual nerve stimulation, leading to paralysis and death. In the IRAC framework, this mechanism places organophosphates in the acetylcholinesterase inhibitors group, distinguishing them from compounds with other targets—like pyrethroids that affect sodium channels or substances that disrupt juvenile hormone pathways. Carbamates also inhibit acetylcholinesterase but belong to a different subgroup, so the specific organophosphate classification is for acetylcholinesterase inhibitors within the IRAC system.