Acaricide resistance test
Acaricide resistance test - Beef CRC - Beef Genetic Technologies
 The CRC has developed a test that can be used to maximise the effectiveness of acaricides (pesticides that kill ticks and mites) and to reduce the amount of acaricides used to control ticks.Associate Professor Nick Jonsson from the University of Queensland has uncovered the genetic mutation which causes ticks to be resistant to synthetic pyrethroids (SPs) in Australia. The mutation is in the same gene as the one which causes resistance to SPs in Latin America. But it is a completely different mutation in Australia. |
| Why does industry want this acaricide test? |
| Using chemicals to control ticks inevitably leads to a build up of resistance and as a result their efficacy decreases. Simple Darwinian evolution indicates in any population there are individuals genetically resistant to certain controls. The frequency of those individuals is very low, usually down to 1 in every 100 million. But with acaricide use there is a greater probability that the individuals which have the mutation are going to survive and reproduce. The more often producers treat cattle, the greater proportion of ticks that carry the mutation and the more rapidly producers select for resistance. Such is the case with the current catalogue of vaccines used to control cattle ticks in northern Australia. Resistance to acaricides is a huge economic cost to the northern beef industry which already spends about $8 million dollars each year in controlling ticks. There are four different groups of acaricides used in Australia. Synthetic pyrethroids (SPs), amitraz, macrocyclic lactones (MLs) and fluazuron. Amitraz is most widely used, but 50 per cent of all the ticks tested are resistant to SPs. Given that SPs and amitraz are the cheapest products, if ticks are resistant to them, producers are forced to use an ML or fluazuron which cost about five to 10 times as much per animal to use. Producers prefer to use products which are cheap and convenient to apply. If a product no longer works, producers either put up with the lower level of efficacy or shift to another, perhaps more expensive product. This means they may sacrifice some control to reduce the overall cost of protecting their herds against ticks. The current technology used to determine whether ticks are resistant to acarcides is called the larval packet test. It is conducted by the Queensland Department of Primary Industries and Fisheries. But it is considered to be time consuming and cumbersome. |
| How will industry benefit from the acaricide resistance test? |
| While the individual producer is unlikely to use this new test, it will assist further research into which strategies can help reduce acaricide resistance. There are several management strategies which are believed to help, but there is not a lot of data to support them. Some people advocate rotating the acaricides. Others believe you should manipulate the dose and use a higher or lower concentration than the recommended dose. People assume this can cause problems but no-one has ever tested it, so there is absolutely no data to say whether these strategies are valuable. Scientists can now test these theories. Further field tests are now dependent on securing research funds. The likelihood of an individual producer wanting to use this test will be enhanced if scientists can develop a similar test which identifies resistance to amitraz or macrocyclic lactones. Work being carried out by PhD student Emily Piper, University of Queensland, could also lead to the development of a clean, green way of controlling cattle ticks. Ms Piper’s research focuses on identifying the mechanisms responsible for “natural” host resistance against cattle ticks. |
| Progress |
| The new molecular test is much quicker than the current bio-assay, which can take up to eight weeks to confirm resistance in ticks. Currently a sample of fully engorged female ticks is collected from a property. They are allowed to produce eggs and the larvae is exposed to several different acaricides to see which ones they are sensitive to. All scientists have to do now is crush the ticks and extract their DNA. They are genotyped to see whether they carry the particular mutation; scientists are almost 100 per cent sure if they carry that mutation they will be resistant to SPs. Associate Professor Jonsson said field tests are now dependent on securing further research funds. |
