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
• 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