How exactly does aerosol insecticides kill the insects?

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Why do they thrash around and appear as if they are having a seizure before dying?

In: Biology

It depends on the specific toxin that’s used. Pyrethroid insecticides, which are the most common in aerosols, are a neurotoxin (meaning it affects nerves).

In order for nerves to transmit a signal, they need to allow the flow of sodium and potassium between the inside and outside of their cell membranes. To put it very simply, by allowing positively charged sodium to enter the neuron at a given time, it will result in the inside of the cell having a more positive charge than the outside. This is the source of the apparent voltage (referred to as a membrane potential) in a neuron. It is a common misconception that nerves act like electrical wires but in reality it’s a little more complex.

Anyway, this flow of sodium is controlled using gated channels, which are basically tunnels that can be opened and closed in response to a stimulus. The transmission of a membrane potential through a neuron is achieved by voltage-gated sodium channels. So once an initial amount of sodium is introduced and the membrane potential changes, these voltage gated sodium channels further down the cell will open in a cascade reaction, bringing more sodium in and hence transmitting the signal further down.

Pyrethroid insectides work by blocking off these voltage gated sodium channels, stopping the inflow of sodium, and therefore preventing the insect’s nervous system from producing a usable potential. This will lead to a lot of side effects (you noted muscular spasms as one), but the part that kills them is when the nerves that control the respiratory system shut down.