Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/2/2008
Publication Date: 2/20/2009
Citation: Chen, A.C., He, H., Temeyer, K.B., Jones, S., Green, P., Barker, S.C. 2009. A survey of Rhipicephalus microplus populations for mutations associated by pyrethroid resistance. Journal of Economic Entomology. 120(1):373-380. Interpretive Summary: The southern cattle tick (SCT) and the disease it transmits, babesiosis, were eradicated from the US after a 50-year eradication program of dipping cattle and temporarily vacating tick-infested pastures. SCT is still widespread in Mexico and other parts of America. Reintroduction of the tick to the US either unintentionally or by active agro-terrorism could prove devastating to cattle industry. Quarantine by vat dipping with chemical acaricides has prevented reinfestation in the US. But SCT has developed resistance to acaricides. There is a real need for rapid, sensitive, and accurate methods for detecting pesticide resistance, which will lead to better pest management strategies and prolong the usefulness of the currently available pesticides. The current method used for resistance detection takes weeks to perform and is laborious. We had previously discovered 2 mutations in resistant ticks. Based on these mutations, we have now developed assays that are sensitive, capable of detecting resistance to certain class of pesticides in individual ticks smaller than a pinhead, and can be performed in just 3 – 4 hours. In addition, because these methods make use of the genetic material of the pest, the potential resistance can be detected even before it is manifested. These assays have been validated on laboratory-reared ticks. In the future, these assays can be used to study the distribution and frequency of tick resistance genes, which will greatly enhance the management of this critical pest.
Technical Abstract: Mutations associated with pyrethroid resistance were found in Mexican strains of Rhipicephalus microplus. A mutation in the sodium channel gene was reported in strains highly resistant to permethrin and another mutation in an esterase gene in a strain that shows moderate resistance to the same pesticide. Methods based on the melting temperature difference of amplified allele-specific DNA fragments were developed that can detect these mutations rapidly in individual larvae. When these methods were applied to ticks from various strains of R. microplus from Australia, neither of these mutations could be demonstrated. Different resistance mechanisms have apparently developed independently between Australian and Mexican strains of R. microplus.