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Pyrethrins and Pyrethroids

Pyrethrins & Pyrethroids

What are pyrethrins?

  • Pyrethrins are insecticides that are derived from the extract of chrysanthemum flowers (pyrethrum).
  • The plant extract, called pyrethrum contains pyrethrin I and pyrethrin II collectively, called pyrethrins.

  • What are pyrethroids?

  • Pyrethroids are synthetic (human-made) forms of pyrethrins. There are two types that differ in chemical structure and symptoms of exposure.
  • Type I pyrethroids include allethrin, tetramethrin, resmethrin, d-phenothrin, bioresmethrin, and permethrin.
  • Some examples of type II pyrethroids are cypermethrin, cyfluthrin, deltamethrin, cyphenothrin, fenvalerate, and fluvalinate.
  • Both type I and II pyrethroids inhibit the nervous system of insects. This occurs at the sodium ion channels in the nerve cell membrane. Some type II pyrethroids also affect the action of a eurotransmitter called GABA.

  • What are pyrethrins and pyrethroids used for?

  • Pyrethrins are widely used for the control of various insect pests.

  • How do pyrethrins and pyrethroids work?

  • Nerve cell membranes have a specific electrical charge. Altering the amount of ions (charged atoms) passing through ion channels causes the membrane to depolarize which, in turn, causes a neurotransmitter to be released. Neurotransmitters help nerve cells communicate. Electrical messages sent between nerve cells allow them to generate a response, like a movement in an animal or insect.
  • Pyrethrins affect the nervous system of insects by causing multiple action potentials in the nerve cells by delaying the closing of an ion channel.
  • Pyrethrins and pyrethroids act as contact poisons, affecting the insect's nervous system.
  • Even though pyrethrins and pyrethroids are nerve poisons, they are not cholinesterase inhibitors like organophosphate or carbamate insecticides.
  • Pesticide products containing pyrethrins usually contain a synergist (such as piperonyl butoxide).
  • Synergists work by restricting an enzyme that insects use to detoxify the pyrethrins. A synergist allows the insecticide to be more effective.

  • How toxic are pyrethrins and pyrethroids?

  • Pyrethrins are one of the least poisonous insecticides to mammals.
  • Rats fed high doses (1,000 milligrams per kilogram of body weight or mg/kg) of pyrethrins showed liver damage.
  • Rats exposed to pyrethrins exhibited difficulty or rapid breathing, incoordination, sprawling of limbs, tremors, aggression, sensitivity to external stimuli, twitching, and exhaustion.

  • What effect does fipronil have on wildlife?

  • Pyrethrins are highly toxic to fish and tadpoles. They affect their skin touch receptors and balance organs.
  • Pyrethrins are toxic to beneficial insect (such as honeybees) and many aquatic invertebrates.
  • Pyrethrins are low in toxicity to humans, other mammals, and birds.

  • Signs of toxicity in humans.

  • Inhaling pyrethrins can cause coughing, wheezing, shortness of breath, runny or stuffy nose, chest pain, or difficulty breathing.
  • Skin contact can cause a rash, itching, or blisters.


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