What is acaricide resistance?

  • A genetic trait that allows resistant ticks to survive acaricide treatments.
  • Resistance is heritable, it is passed on from parents to offspring.
  • Resistance to one chemical group does not usually confer resistance to an unrelated chemical group.
  • There is usually cross resistance between different chemical actives in the same chemical group. Changing between products that contain actives from the same chemical group won’t help manage resistance.
  • Under dosage, poor application, unnecessary treatments and repeated use of the same chemical group can lead to increased resistance in parasite populations.

Acaricide resistance is a genetic change (mutation) in individual ticks within a parasite population that allows resistant ticks to survive treatment. Because it is genetically based, resistance to the same chemical group is passed on to the next generation.

There are a number of ways that resistance is expressed. For example, gene mutations that block the active have been shown to be responsible for most resistance to synthetic pyrethroids (SPs) in ticks and it is likely the main mechanism for resistance to amitraz. In contrast, detoxification mechanisms in ticks have been shown to be important for organophosphates (OPs) and to a lesser extent for SPs.

Resistance is heritable, meaning that resistance is passed on from one generation to the next. Repeated use of the same chemical group can cause ongoing selection of the more resistant parasites, as susceptible types are killed. If the relative proportion of resistant ticks in the population increases compared to susceptible ticks, and the resistant ticks come to dominate, then the effectiveness of the chemical to control the parasite will become compromised.

Importantly, resistance to different chemical groups occurs through different mutations within the ticks. As a result, resistance to one chemical group does not usually equate to resistance to other chemical groups. However, resistance against an active within a chemical group, will confer resistance (though not necessarily to the same extent) to all other actives within the same chemical group. Avoid repetitive use of actives within the same chemical group to reduce the build-up of resistant individuals within populations.

Figure 1. Chemical resistance can build in a tick population if products are under-dosed, are applied poorly, ticks are exposed to unnecessary treatments, or if actives from the same chemical group are repetitively used. Image courtesy of Jess Morgan
Figure 1. Chemical resistance can build in a tick population if products are under-dosed, are applied poorly, ticks are exposed to unnecessary treatments, or if actives from the same chemical group are repetitively used. Image courtesy of Jess Morgan