ORIGINAL PAPER Acetylcholinesterase 1 in populations of organophosphate-resistant North American strains of the cattle tick, Rhipicephalus microplus (Acari: Ixodidae) Kylie G. Bendele 1 & Felix D. Guerrero 1 & Robert J. Miller 2 & Andrew Y. Li 3 & Roberto A. Barrero 4 & Paula M. Moolhuijzen 4 & Michael Black 4 & John K. McCooke 4 & Jason Meyer 5,6 & Catherine A. Hill 5 & Matthew I. Bellgard 4 Received: 18 December 2014 /Accepted: 28 April 2015 /Published online: 8 May 2015 # Springer-Verlag Berlin Heidelberg (outside the USA) 2015 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- US border even though the tick has been eradicated from the USA. The organophosphate (OP) coumaphos targets acetyl- cholinesterase (AChE) and is the approved acaricide for erad- icating cattle fever tick outbreaks. There is evidence for cou- maphos resistance developing in cattle ticks in Mexico, and OP-resistant R. microplus ticks were discovered in outbreak populations of Texas in 2005. The molecular basis of couma- phos 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 al- lele diversity in tick populations with different levels of cou- maphos 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 man- agement 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 Electronic supplementary material The online version of this article (doi:10.1007/s00436-015-4505-0) contains supplementary material, which is available to authorized users. * Felix D. Guerrero felix.guerrero@ars.usda.gov Kylie G. Bendele Kylie.Bendele@ars.usda.gov Robert J. Miller Robert.Miller@ars.usda.gov Andrew Y. Li Andrew.Li@ars.usda.gov Roberto A. Barrero rbarrero@ccg.murdoch.edu.au Paula M. Moolhuijzen pmoolhuijzen@ccg.murdoch.edu.au Michael Black mblack@ccg.murdoch.edu.au John K. McCooke jmccooke@ccg.murdoch.edu.au Jason Meyer hessianfly@yahoo.com Catherine A. Hill hillca@purdue.edu Matthew I. Bellgard mbellgard@ccg.murdoch.edu.au 1 USDA-ARS Knipling-Bushland U. S. Livestock Insects Research Laboratory, 2700 Fredericksburg Road, Kerrville, TX 78028, USA 2 USDA-ARS Cattle Fever Tick Research Laboratory, 22675 North Moorefield Road, Building 6419, Edinburg, TX 78541, USA 3 USDA-ARS Invasive Insect Biocontrol and Behavior Laboratory, 10300 Baltimore Avenue, Beltsville, MD 20705, USA 4 Centre for Comparative Genomics, Murdoch University, Murdoch, WA 6150, Australia 5 Department of Entomology, Purdue University, West Lafayette, IN 47907, USA 6 Biotechnology Division, Monsanto Company, 700 Chesterfield Parkway West, Chesterfield, MO 63017, USA Parasitol Res (2015) 114:3027–3040 DOI 10.1007/s00436-015-4505-0