Skip to main content
ARS Home » Plains Area » Kerrville, Texas » Knipling-Bushland U.S. Livestock Insects Research Laboratory » LAPRU » Research » Publications at this Location » Publication #312859

Research Project: Genomics of Livestock Pests

Location: Livestock Arthropod Pests Research

Title: Acetylcholinesterase 1 in populations of organophosphate-resistant North American strains of the cattle tick, Rhipicephalus microplus (Acari: Ixodidae)

Author
item Bendele, Kylie
item Guerrero, Felicito - Felix
item Miller, Robert
item Li, Andrew
item Barrero, Roberto - Murdoch University
item Moolhuijzen, Paula - Murdoch University
item Black, Michael - Murdoch University
item Mccooke, John - Murdoch University
item Meyer, Jason - Purdue University
item Hill, Catherine - Purdue University
item Bellgard, Matthew - Murdoch University

Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2015
Publication Date: 7/27/2015
Publication URL: http://handle.nal.usda.gov/10113/61882
Citation: Bendele, K.G., Guerrero, F., Miller, R., Li, A.Y., Barrero, R., Moolhuijzen, P., Black, M., Mccooke, J., Meyer, J., Hill, C., Bellgard, M. 2015. Acetylcholinesterase 1 in populations of organophosphate-resistant North American strains of the cattle tick, Rhipicephalus microplus (Acari: Ixodidae). Parasitology Research. 114(8):3027-3040.

Interpretive Summary: Rhipicephalus microplus, the cattle fever tick, is a global economic problem to the cattle industry due to direct infestation of cattle and pathogens transmitted during feeding. The tick has been eradicated from the U.S., however, tick outbreaks continue to occur along the Mexico-U.S. border. The organophosphate (OP) coumaphos is the approved acaricide for eradicating cattle fever tick outbreaks. Coumaphos exerts its anti-tick activity by inactivating a protein ensymatic activity known as acetylcholinesterase (AChE) that degrades the neurotransmitter acetylcholine. Ticks have a great capacity for developing resistance to acaricides and there is evidence for coumaphos resistance developing in cattle ticks in Mexico. Alarmingly, coumpahos resistant R. microplus ticks were discovered in outbreak populations of Texas in 2005 and since. The molecular basis of coumaphos resistance is not known and our study was established to gather further information on whether the AChE1 protein is involved in the resistance mechanism. We also sought information on AChE1 sequence diversity in tick populations with different levels of coumaphos resistance. The overarching project goal was to identify AChE1 mutations that caused coumaphos resistance. If these mutations existed and were identified, a DNA-based diagnostic assay would be developed to assist the management of resistance. Here, we report the sequence for the R. microplus AChE1 gene ascertained by sequencing. We also report AChE1 sequences of larval ticks from R. microplus strains having different sensitivities to coumaphos. We identified 72 different AChE1 sequence variants, 2 of which were common in the populations containing coumaphos resistant ticks.

Technical Abstract: Rhipicephalus microplus, the cattle fever tick, is a global economic problem to the cattle industry due to direct infestation of cattle and pathogens transmitted during feeding. Cattle fever tick outbreaks continue to occur along the Mexico-U.S. border even though the tick has been eradicated from the U.S. The organophosphate (OP) coumaphos targets the enzyme acetylcholinesterase (AChE) and is the approved acaricide for eradicating cattle fever tick outbreaks. There is evidence for coumaphos resistance developing in cattle ticks in Mexico, and OP resistant R. microplus ticks were discovered in outbreak populations of Texas since 2005. The molecular basis of coumaphos resistance is not known and our study was established to gather further information on whether AChE1 is involved in the resistance mechanism. We also sought information on allele diversity in tick populations with different levels of coumaphos resistance. The overarching project goal was to define OP resistance-associated gene mutations such that a DNA-based diagnostic assay could be developed to assist the management of resistance. Three different AChE transcripts have been reported in R. microplus, and supporting genomic and transcriptomic data are available at CattleTickBase. Here, we report the complete R. microplus AChE1 gene ascertained by sequencing a bacterial artificial chromosome clone containing the entire coding region and the flanking 5' and 3' regions. We also report AChE1 sequences of larval ticks from R. microplus strains having different sensitivities to OP. To accomplish this, we sequenced a 669 bp region of the AChE1 gene corresponding to a 223 amino acid region of exon 2 to assess alleles in seven strains of R. microplus with varying OP resistance phenotypes. We identified 72 AChE1 sequence variants, 2 of which are strongly associated with OP resistant phenotypes. Esterase-like sequences from the R. microplus transcriptome RmiTr Version 1.0 were compared to the available sequence databases to identify other transcripts with similarity to AChE1.