Boophilus microplus is an economically significant tick parasite of cattle, responsible for severe negative impacts on animal health and cattle producer profitability in many regions of the world. Our research group has begun the development of molecular-based assays for specific acaricide resistance-associated genes to facilitate the identification of acaricide resistant populations of B. microplus. We have devised a PCR-based assay to detect a specific sodium channel gene mutation that is associated with resistance to permethrin. A number of Mexican strains of B. microplus have been genotyped by this assay that can be performed on individual ticks at any life stage with results available in a few hours. Additionally, a specific metabolic esterase with permethrin-hydrolyzing activity has been purified and its gene coding region cloned. A mutant allele of this esterase gene has been found, though the mutation seems to provide only a low level of additional permethrin resistance compared to that provided by the wild type allele. Work is continuing to clone specific acetylcholinesterase (AChE) and carboxylesterase genes that appear to be involved in resistance to organophosphates (OP). We are designing a battery of DNA-or ELISA-based assays capable of rapidly genotyping individual ticks for pyrethroid and OP resistance-associated genes.
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