Tag Archives: insecticides

Mosquito

How Do Pesticides Work?

Pesticides refer to both insecticides and herbicides which are used to kill unwanted insects or plants, respectively. They work by disrupting chemical pathways in important metabolic processes. Most are believed safe for humans but best practice is to avoid repeated high doses.

How Does Permethrin Work?

Permethrin is an insecticide derived from compounds similar to those found naturally in chrysanthemums. It is used on a variety of insects including mosquitoes and head lice and acts as a neurotoxin.

As explained in this Toxipedia article1 , permethrin makes the host’s nervous system hypersensitive to stimuli by binding to sodium ions. This can cause increases in body temperature to which cold blooded organisms such as insects and amphibians are more susceptible. Mammalian livers readily break permethrin down and the resulting metabolites are rapidly excreted.

Permethrin insectide
Permethrin is similar to compounds found in chrysanthemums.

How Does Glyphosate Work?

Glyphosate is a herbicide designed to prevent the growth of weeds that compete with cultivated crops such as corn, soy, canola and cotton. It is otherwise a broad spectrum chemical that can kill other plants such as lawn grass and desirable garden plants.

It targets plant enzymes involved in the production of several amino acids and is most effective when applied once the weeds are actively growing. These enzymes are specific to plants and because humans and other animals get these amino acids from the foods they eat,  the overall risk to health is considered low.

Glyphosate is a chemical that interferes with amino acid production in plants.
Glyphosate, aka Roundup, interferes with amino acid production in plants.

How Does Malathion Work?

Malathion is an insecticide that has been used to combat a variety of pests ranging from fruit flies to mosquitoes. It acts on an enzyme called acetylcholinesterase which mediates the effects of the neurotransmitter acetylcholine 2 . Acetylcholine in turn regulates muscle activity under control of the nervous system.

Malathion is a potent neurotoxin, similar in action to nerve gas such as Sarin. In common practice, Malathion is used at concentrations not considered toxic to  humans but since this biochemical pathway is common to virtually all animals, safe handling is important.

Malathion

How Does DDT Work?

At one time DDT was considered a valuable pesticide in the control of mosquitoes that carried dangerous diseases such as malaria and typhus. It acted by causing  uncontrolled firing of nerve impulses that resulted in spasms and death.

While not very toxic to humans, DDT was found to concentrate in the food chain & was particularly harmful to top predators such as eagles. condors and falcons. DDT caused  thinning of bird eggshells which in turn increased mortality in their offspring.  For this reason, the pesticide was largely banned worldwide by the 1980s.

DDT
Pesticides are a convenience that we would it hard to live without. While they can be considered safe if used occasionally & according to instructions, caution should still be taken. Don’t handle concentrates without gloves. If you do get them on your skin, wash them off with soap. Do not make a habit of spraying upwind.

References

  1. Toxipedia. See: Pharmacology & Metabolism of Permethrin.
  2. Wikpedia. See:  Acetycholine for a  more detailed explanation.
  3. Wikipedia. See: DDT Mechanism of Action