Organophosphates (OP)

What do they treat?

Flies Ticks Lice

When using OPs 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 pesticide resistance to all of these parasites each time an OP product is used.

Note:  Toxic to humans

How can they be administered?

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

Ear tags Spray on Dip Backrubber Powder

Premises surface spray Premises paintable bait

  • Ear tags, spray on, pour-on and dips should be correctly applied to all cattle in a mob to ensure effective control.
  • Only use powder to treat animals affected by flystrike.


Reported in: Flies Ticks

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.

  • Toxic to humans.
  • Occupational health and safety risks necessitate greater care during storage, use and disposal of OPs.
  • OPs may be absorbed through human skin, inhaled in vapours or absorbed by ingestion.
  • Absorption is enhanced by moisture on the skin surface (e.g. sweat or contaminated clothes).
  • OPs are readily absorbed through breaks in the skin, such as cuts, cracked skin and sores.
  • Use appropriate personal protective equipment (PPE) for application method.


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 intervals (ESI) periods. Current ESI periods can be confirmed on the APVMA website.

Types of organophosphate

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

Table 1. Organophosphates 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)






Buffalo fly Stable fly

Premises flies*

Fly strike

Cattle tick Paralysis tick Bush tick







































































Combination (same target boxed)


Chlorfenvinphos and cypermethrin


Buffalo fly


Cattle and other ticks


Ethion and deltamethrin


Buffalo fly


Cattle  and bush tick


Diazinon and pyrethrins


*IRAC Mode of Action group 1B

What are they?

Organophosphates (OPs) are synthetic chemicals that belong to the organic esters of phosphoric acid. OPs kill insects by altering their normal neurotransmission.

How do they work?

OPs have a broad spectrum of activity.

Most OPs act by contact with the insect—a few are also systemic. OPs exert their effects on the nervous system of organisms. As such, they are relatively fast-acting and susceptible insects will be killed within 4–8 hours of exposure.

OPs cause accumulation of acetylcholine (ACh) by blocking the enzyme (acetylcholinesterase) which normally breaks down this neurotransmitter. ACh is common to both insects and mammals and as a result, OPs are toxic to humans.