Resistance in Cattle Ticks

Cattle ticks are a costly pest across northern Australia. Producers rely on chemical treatments to control tick numbers, but resistance to the common chemical groups has made them ineffective. Resistant ticks can be diagnosed in the laboratory by collecting engorged ticks. Avoid resistance by using Integrated Pest Management, including genetic selection, vaccination for tick fever, paddock management and genetic selection. Combinations of chemicals and rotating chemicals can be used if frequent treatments are conducted.

What are resistant ticks?

Cattle ticks (Rhipicephalus australis) spread tick fever, cause hide damage and slow down growth rates of cattle. Producers use chemicals to keep tick numbers under control. However, ticks adapt genetically and rapidly develop ways of living with our chemical treatments.

Acaricide resistance was first identified in Queensland in 1937, 40 years after the introduction of arsenic dips.  Since then, organochlorines (DDT), organophosphates, carbamates, amidines (amitraz) and synthetic pyrethroids have all been used in dips and sprays and fluazuron in a pour-on application. All these chemicals have developed some level of resistance, on average 10-20 years after the release of the chemical class.

Resistance has also been seen to fipronil and spinosad in cattle ticks overseas, but these chemicals have not yet been registered for use against cattle ticks in Australia. What is worse, cattle ticks in Central and South America have developed resistance to the mectins (macrocyclic lactones or MLs), a class of chemical used widely in Australia to control ticks. Over-reliance on this chemical class could lead to resistance in cattle ticks here as well.

Table One – Chemical groups for treatment of cattle ticks- (see ParaBoss Product Search Tool)

NB: Some applications not registered for treatment of cattle ticks (*)

Testing for chemical-resistant ticks

Cattle producers are encouraged to contact their local Biosecurity Officer or private veterinarian prior to submitting samples. Ticks can be tested for resistance to the chemical groups listed in Table One (above). Queensland Biosecurity Laboratory carries out two different types of resistance tests (‘bio-assays) for cattle ticks.

The fluazuron test is called the ‘Adult Tick Immersion Test’, which requires female ticks that are engorged but not yet laying eggs. The knockdown chemicals are tested using the ‘Larval Packet Test’. Results are generally available in 7-8 weeks.

Tick sampling checklist

1. Contact your vet or Biosecurity Officer to let them know you will be sending samples.
2. Collect before treatment (or at least 49 days after).
3. The right ticks are the ‘engorged’ ones about 10mm long and round, not the smaller, flatter ‘unengorged’ ticks.
4. Pluck engorged ticks (minimum 30 but preferably 60) gently from several animals.
5. Place in a small, non-crushable carboard or plastic container with air holes in the lid, with a few blades of grass (just a few!) to provide some moisture. Keep in shade.
6. Place securely in esky or strong cardboard box (with wrapped ice brick in hot conditions) and send immediately to lab by courier.

How to prevent resistant ticks

The right combination of methods is different for each property.

1. Cattle genetics – e.g. use tick-resistant breeds of tropical cattle that have natural immunity to ticks
2. Strategic treatments in spring and early summer to suppress build-up of tick numbers, as well as in autumn to prevent ticks ‘over-wintering’
3. Allow larval ticks to die out, by spelling paddocks and controlling feral tick hosts (e.g. deer, un-mustered cattle)
4. Rotate chemical groups and use combination products
5. Ensure correct dose for pour-on or injectable products and complete coverage of chemical when dipping or spraying cattle (see product label for directions).

Summary

Resistance is common in cattle ticks and is a critical cause of production loss and death of northern cattle. You can submit ticks to the laboratory to work out what chemicals still work on your property. Avoid chemical resistance by using non-chemical means of control and rotating treatments.

See TickBoss for more information about cattle ticks and their prevention, or read the MLA Feedback Magazine Summer 2021 edition for more information.