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Home Synthetic Pyrethroids and Pyrethrins (SP)

Synthetic Pyrethroids and Pyrethrins (SP)

What do they treat?

√ Flies √ Ticks √ Lice

When using SPs to target a particular parasite, be aware that they will be treating any other of the above-mentioned parasites that are present. This can increase the development of chemical resistance by all of these parasites each time an SP product is used.

Note: √ Very toxic to fish and to beneficial insects such as bees

How can they be administered?

√ Ear tags √ Spray on √ Pour on √ Dip √ Powder √ Premises surface spray

A variety of application methods for administering pesticide products to cattle are in use.

  • Ear tags, spray on, pour on and dips should be correctly applied to all cattle in a mob to ensure effective control.
  • Follow label instructions.


Reported in: √ Flies / Ticks

  • SP resistance has been detected in certain areas and once present it can build up very quickly.
  • Under-dosing will lead to poor pest control and may hasten the development of resistance to the chemical.

What is resistance?


Everyone working in the rural industry has a ‘duty of care’; a legal obligation to provide a safe workplace for everyone on the property.

  • SPs and pyrethrins are generally regarded as compounds of low-toxicity but can cause eye and skin irritation in some people.


Withholding periods are mandatory with all registered veterinary products used to treat animals for internal and external parasites.

  • Always check the product label before use for specific withholding periods (WHP) and export slaughter interval (ESI) periods. Current ESI periods can be confirmed on the APVMA website.

Types of synthetic pyrethroids and pyrethrins

A guide to the different actives and the pests they affect are in Table 1. See the Products Search Guides for LiceBossWormBossTickBoss and FlyBoss for the appropriate formulation and application method for your target pest. Note combinations and mixtures of actives may improve treatment efficacy.

Table 1. Synthetic pyrethroids and pyrethrins, their actives, combinations and mixtures and a summary of the targeted parasites for which formulations are registered for. Boxed check marks indicate the pest targeted by multiple actives.

Pests targeted (may vary with formulation)
Worms Flies Ticks Lice Mites
Buffalo fly Stable fly Premises flies* Fly strike Cattle Paralysis Bush
Combination (all actives target boxed parasite)
Beta-cyfluthrin and imidacloprid
Cypermethrin and chlorfenvinphos Buffalo fly √ Cattle √ and other ticks
Cyphenothrin and detla-tetramethrin
Deltamethrin and ethion Buffalo fly √ Cattle √ and bush tick
Pyrethrins and diazinon

*IRAC Mode of Action group 3A

What are they?

Synthetic pyrethroids are synthetically manufactured compounds with a molecular structure similar to naturally occurring pyrethrins. Natural pyrethrins are extracts from the flowers of certain plants which have insecticidal and repellent properties.

How do they work?

SPs have a broad spectrum of activity, they are non-systemic, very fast-acting chemicals that act by contact. Susceptible insects are knocked down and die very quickly. Many SPs and pyrethrins also have a repellent effect.

SPs affect the axons of nerves causing paralysis of target organisms by keeping sodium channels open in the nerve membranes. The resultant constant nerve excitement eventually causes insect paralysis. This toxic effect also occurs in vertebrates since the cellular membranes work in a similar manner.

Natural pyrethrins are unstable when exposed to sunlight limiting protection for animals to a few days at most.

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