ARS | Publication request: Novel approaches for control of Rhipicephalus (Boophilus) microplus

Submitted to: J Tecnica Pecuaria En Mexico
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 21, 2010
Publication Date: October 8, 2012
Citation: Temeyer, K.B., Chen, A.C., Davey, R.B., Guerrero, F., Freeman, J.M., Kammlah, D.M., Li, A.Y., Lohmeyer, K.H., Olafson, P.U., Perez De Leon, A.A., Phillips, P.L., Pound, J.M., Welch, J.B. 2012. Novel approaches for control of Rhipicephalus (Boophilus) microplus. J Tecnica Pecuaria En Mexico. 3(Suppl. 1):25-40.

Interpretive Summary: The Cattle Fever Tick Eradication Program (CFTEP) succeeded in eliminating cattle fever ticks (CFT) from the United States in 1943. These ticks remain endemic in Mexico and transmit two often fatal diseases to cattle that have not developed immunity. Approximately a million cattle are imported into the U.S. from Mexico each year, each of which is treated with acaricide and hand inspected to be certain that no CFTs enter the U.S. Mexican ticks have developed resistance to many acaricides, which threatens the ability to keep them from becoming reestablished in the U.S., where they would be a major threat to the livestock industry. The Knipling-Bushland U.S. Livestock Insects Laboratory and the Cattle Fever Tick Research Laboratory are charged with providing research support to the CFTEP to ensure its continuing success in keeping the U.S. free of CFTs. Research programs and accomplishments are described that enable continuing development of new materials, procedures, equipment, and knowledge to deal with changing conditions in South Texas that threaten the CFTEP. One major challenge that greatly influences success of the CFTEP is a large increase in the population of deer and other wild ungulates that are capable of serving as alternative hosts to spread and maintain tick populations. Research to understand the interaction between the tick and its animal hosts, tick molecular genetics, toxicology and physiology is directed to gain knowledge that enables development of new control technologies, many of which are described in this report.

Technical Abstract: We review recent progress for control of Rhipicephalus (Boophilus) microplus and R. (B.) annulatus. Outbreak infestations in the U.S. have reached alarming levels, due to increased populations of deer and other ungulates serving as alternative hosts. GIS mapping of infestations and deer habitat aids in utilizing methods and equipment designed for acaricide treatment of wild ungulates. Investigations include deer immunology, tick molecular genetics, acaricide resistance, and host-parasite interactions with deer or cattle, ticks, and pathogens. Acaricide resistance is widespread in Mexico and U.S. dipping vats depend on organophosphate (OP) inhibition of acetylcholinesterase (AChE). Three cDNAs putatively encoding acetylcholinesterases (AChE, E.C. 3.1.1.7) in R. (B.) microplus were expressed in the baculovirus system and exhibited Km values for acetylthiocholine of approx. 5, 50, or 90 µM, for rBmAChE1, rBmAChE2, and rBmAChE3, respectively. The rBmAChEs exhibited substrate preference for acetylthiocholine over butyrylthiocholine, and inhibition by eserine, paraoxon, and the AChE-specific inhibitor, BW284C51, confirming biochemical identification as AChEs. Expression of specific mutations from OP-resistant strains exhibited decreased sensitivity of rBmAChE1 and rBmAChE3 to OP inhibition. Each of the BmAChEs were expressed in synganglion as indicated by qRT-PCR. Multiple transcripts from individual ticks for each of the BmAChEs suggested alternative splicing or gene duplication. Quantitative real time PCR with genomic DNA supported the gene duplication hypothesis. Long dsRNA specific for BmAChE1, BmAChE2, and BmAChE3 was introduced by microinjection of unfed adult females and subsequent gene silencing was monitored by qRT-PCR and phenotypic effects. Specific physiological roles for BmAChE1, BmAChE2, and BmAChE3 remain to be elucidated.