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Krishna: The word “Repellent” is not equal to “Insecticide”.

It is important to note that under the general term ‘bug or insect spray’ there are two subgroups: repellent that deters bugs and insecticides that kill bugs.

Repellents do not kill mosquitoes and other insects, but they will help deter them from biting people.

Repellents are substances that help people avoid mosquito bites. Anyone working or playing in mosquito-infested areas will find repellents very helpful. Repellents are formulated for use on bare skin. They are sold as aerosols, creams, solids (sticks),pump sprays and liquids.

Repellents are mostly products that you put on your skin, meaning that they don’t kill bugs but, rather, keep them away from you. The way they do this is quite clever, they mask your scent. Your scent is made up of the chemicals, products and perfumes you use as well as the naturally occurring carbon dioxide you make, released when you exhale, via pores and sweat. Mosquitos and other insects are able to track that CO2 to find ‘food’ (you). So, by putting on insect repellent you are disguising your scent to essentially become ‘invisible’ to hunting insects. Some repellents go even further to make you smell repulsive to bugs which will help keep them away from you!

On the other hand, if you spray insecticide which quickly soaks the cockroach, mosquito or any other insect —the chemicals quickly enter its nervous system and cause its legs and body to twitch, spasm and eventually it lays motionless, dead. Insecticides kill insects. Yes!

It is important to note that these insecticides are not only harmful to insects but can also be toxic to birds, bees and even fish. Factors such as the surface you are spraying on, the chemicals in the spray, the weather, and time can affect the efficiency and duration of action of the insecticide.

The active ingredients of insecticide sprays will cause death differently (1):

  • Pyrethroids are synthetic copies of pyrethrins which are natural compounds found in chrysanthemum flowers. Pyrethroids are neurotoxic, so once it enters the insect’s body it targets neurons. Specifically, they target proteins that transport sodium and potassium across the neuron’s membrane. Neurons are in charge of transmitting messages to and from the brain, and they do this by controlling the entry and exit of sodium and potassium, so the insecticide affecting the transport proteins for these ions essentially stops the signals and paralyses the insect.
  • Organochlorides work by opening sodium ion channels in neurons causing them to spontaneously fire, and resulting in the insect going into spasms and eventually dying.
  • Organophosphates and carbamates target an insect’s nervous system, specifically the enzymes cholinesterase and other cholinesterases. It disrupts nerve impulses and stops neurons from communicating with each other, thus disabling or killing the insect.
  • Neonicotinoids are a synthetic version of nicotine, a natural insecticide. They are acetylcholine receptor agonists that compete with acetylcholine for the same receptor and stops the binding of acetylcholine to the receptor. This causes leg tremors, rapid wing motion, disoriented movement, paralysis and eventual death of the insect.
  • Butennolides are a similar mode of action to neonicotinoid.
  • Ryanoids are synthetic versions of ryanodine. It binds to calcium channels in cardiac and skeletal muscle blocking nerve transmission, so the muscle cells lose function and slow or stop beating.

Footnotes:

Bug spray: Repellents vs insecticides | Grok

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