Why Do Ticks Become Resistant To Acaricides?

Acaricides are chemical compounds used to kill acarids, which include ticks and mites.

Cattle tick-resistance to acaricides refers to the ability of ticks to survive, despite the adverse effects of acaricides.

When ticks survive death by acaricides, they pass on this genetic capability to their offspring. Initially, this resistant gene is low in a tick population.

However, with continued use of the chemical, a population of resistant ticks develops. This means the acaricide used becomes ineffective in killing and controlling cattle ticks. This reduces the number of available effective acaricides on the market.

The ‘ideal’ acaricide is one that:

• Can be easily administered by a number of methods such as pour-on, plunge-dip, spray
• Dip or injection.
• Is rapidly metabolised and excreted to reduce the level of chemical residue in the animal.
• Has a high level of toxicity towards all stages of the lifecycle of cattle ticks.
• Is cost-effective

Factors that influence acaricide resistance

• Treatment frequency: The more ticks are exposed to the chemical, the more likely they will develop resistance to it.
• Underdosing increases the risk of tick survival.
• Persistent use of one chemical group for tick control.

How to reduce risk of acaricide resistance

• Always use the recommended strength of acaricides in dips as stated by the manufacturer.
• If using a plunge dip, always re-dip your stirrer cattle.
• Never under-dose animals during treatment with pour-on or injectable applications. Treat the mob at the rate of the heaviest animal, reducing the chance of under-dosing.
• Import only tick-free livestock to your farm/ premises. If this is unavoidable, treat livestock on arrival and only allow tick-free cattle onto the paddock.
• If you suspect poor tick kill, notify your local veterinary officer for investigation and testing of the acaricide.