Insecticides kill their target insect species in a variety of ways. Two of the most commonly used classes of insecticide are the organophosphates (nerve gases) and the carbamates. These compounds act quickly (in a matter of hours), are lethal at low doses (parts per billion), degrade rapidly (in hours to days) and leave few toxic residues in the environment. Organophosphates kill insects by inducing loss of control of the peripheral nervous system, leading to uncontrollable spasms followed by paralysis and, ultimately, death. This is often accomplished by a biochemical process called cholinesterase inhibition.

Most animals' nervous systems are composed of individual nerve cells called neurons. Between any two adjacent neurons there is always a gap, called the synaptic cleft; the neurons do not actually touch each other. When an animal senses something—for example, pain—the sensation is transmitted chemically from one neuron to another until...