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Mode of action of Neonicotinoids

Karl Foord, Extension Educator - Horticulture


Insecticides can be characterized by the way in which they disrupt important biochemical functions. Many insecticides target the nervous system of insects by impairing the control of neural transmission. This can be done by disabling the system, and shutting it down. However, the majority of neural insecticides put the system in a continual state of ON giving the organism no opportunity to stop neural transmission. This results in uncontrolled and uninterrupted nerve firing. The insect that is exposed to such chemicals exhibits tremors, hyperactivity and convulsions. Sublethal doses of these chemicals can impair proper functioning behaviors such as flight orientation, and feeding while greater doses lead to a quicker death.

Normal neural transmission

A normal neural transmission proceeds down the nerve axon which splits into branches and eventually into smaller branches called dendrites. The dendrites of one nerve cell pair with the dendrites of other cells. The space between these two dendrites is call a synapse (Exhibit 1).

The electrical signal of the nerve is translated into a chemical message made up of so called neurotransmitter molecules. These molecules diffuse across the synapse and attach to receptor molecules on the dendrites of the paired nerve (Exhibit 2). The chemical message is translated back into an electrical message that then travels down this nerve cell's axon, and the neurotransmitter molecules are disassociated from the receptor molecules by an enzyme.

Neonicotinoid disruption of neural impulse

Neonicotinoid molecules enter the neural synapse and irreversibly attach to the receptors on the receiving neuron (Exhibit 2). The neurotransmitter enzyme cannot remove the imidacloprid molecule and the receptor is thus continuously active. The organism has lost control of neural transmission and either loses function or dies.
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