"The effect of organophosphates was discovered in the 1930's during World War II. They were used in the creation of nerve gas, which was used in chemical warfare. When used in lethal dosages for humans, organophosphates cause extreme excitability, convulsions, paralysis and in most cases, death.
Likewise, pesticides work by affecting the nervous system of the insect. The pesticide interrupts the information being sent by neurotransmitters in the synapses. The chemical produced by the body used to send information through the synapses is called acetycholine. An enzyme called cholinesterase binds with acetycholine and allows muscles to rest.
In a body that is working normally, the acetycholine sends messages to the muscles through the synapses. Cholinesterase keeps the amount of acetycholine at an acceptable level, which controls the stimulation. When a pesticide is introduced at a lethal dosage for a particular body, the cholinesterase is affected, keeping it from binding with the acetycholine. When this happens, the muscles are over-stimulated which will lead to paralysis and death."
On the subject of whether insects have the ability or not to feel pain, I would submit the following facts:
A. The old Boy Scout Handbook from the 1960’s that recommended the use of a recently extinguished match head to make an embedded tick un-embedd itself from the skin.
B. The use of salt on snails and slugs and their writhing reactions as they produce huge amounts of mucus to protect themselves.
C. The use of warps and hornet spray (Raid or Black Flag) on a net of these social insects and their writhing reactions in a death struggle as these nerve agents kill as in this You Tube video.
D. Turn on an eye on a flat surface electric stove. Place a crawling insect facing the burner and the insect will always move away from the eye and never to it or over it.
E. The use of smoke to drive bees from their hives or the use of a smoldering piece of cloth to keep mosquitos away. Smoke is an irritant or pain causing agent.
F. The fact that an insect uses a stinger to inject a painful toxin to protect their net or themselves reveals an understanding of pain.