Mode of action: Neonicotinoids, like nicotine, bind to nicotinic acetylcholine receptors of a cell and triggers a response by that cell. In mammals, nicotinic acetylcholine receptors are located in cells of both the central and peripheral nervous systems. In insects these receptors are limited to cells of the CNS. While low to moderate activation of these receptors causes nervous stimulation, high levels overstimulate and block the receptors. This receptor blockage causes paralysis and death. Nicotinic acetylcholine receptors are normally activated by the neurotransmitter acetylcholine. Normally, acetylcholine is broken down by acetylcholinesterase to terminate signals from these receptors. However, acetylcholinesterase cannot break down neonicotinoids, and the binding is irreversible. Because most neonicotinoids bind much more strongly to insect neuron receptors than to mammal neuron receptors, these insecticides are selectively more toxic to insects than mammals.
via Neonicotinoid - Wikipedia, the free encyclopedia.