Phenome of Acaricide Resistance in the Southern Cattle Fever Tick, Rhipicephalus microplus: Molecular Marker Development

The southern cattle fever tick (CFT), Rhipicephalus microplus, is regarded as the most economically important ectoparasite of livestock, principally cattle, worldwide. The U.S. officially declared the eradication of this invasive tick species in 1943. However, outbreaks still occur in the Permanent Quarantine Zone spanning a region in south Texas that borders northeast Mexico. A limitation for sustainable eradication in the U.S. is the emergence of acaricide resistance among CFT outbreak populations. Molecular diagnostic tools offer the opportunity to detect resistance rapidly, which can be complemented with confirmatory bioassay data that are more resource and time consuming to generate. Here, we report research on the innovation of molecular methods to detect mutations associated with CFT acaricide resistance. Genomic DNA fragments linked to acaricide target site genes (voltage-sensitive sodium channel for pyrethroids, gaba-gated chloride channel for fipronil, and octopamine receptors for amitraz) were amplified by PCR from resistant reference CFT from Brazil and Mexico. Sequencing analysis revealed multiple SNPs in the target site genes from geographically distinct lineages with different resistance phenotypes. This information will be used for high-resolution melting analysis of DNA fragments to develop a high-throughput method to genotype and detect allele-specific mutations in CFT outbreak populations to inform acaricide resistance management strategies in the U.S. This knowledge could also be adapted to integrated control programs in other parts of the world where CFT are endemic.