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Title: Characterization of permethrin-resistant Boophilus microplus (Acari:Ixodidae) collected from the State of Coahuila, Mexico

item Miller, Robert
item George, John

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2007
Publication Date: 9/10/2007
Citation: Miller, R., Esparaza Rentaria, J.A., Quiroz Martinez, H., George, J.E. 2007. Characterization of permethrin-resistant Boophilus microplus (Acari: Ixodidae) collected from the State of Coahuila, Mexico. Journal of Medical Entomology. 44(5):895-897.

Interpretive Summary: The southern cattle tick, Boophilus microplus, is kept out of the United States by the successful execution of the Cattle Fever Tick Eradication Program administered by USDA, APHIS, VS. This program relies heavily on the human inspection of cattle within a quarantine zone along the Texas-Mexico border and the chemical treatment of tick-infested cattle. However, resistance to chemical pesticides has been developing in populations of Mexican southern cattle ticks for the past 25 years. This paper described the characterization of a pyrethroid resistant population of southern cattle ticks collected in Coahula, Mexico very close to the U.S. quarantine zone. Experiments were preformed using several types of pesticides and a polymerase chain reaction procedure (PCR) to determine the mechanisms involved in resistance. It was found that enzymatic activity was not a major mechanism of resistance. However, PCR was used to determine that a mutation of the sodium channel gene was the major cause of resistance in this population. The results of this work benefit both the Cattle Fever Tick Eradication Program and cattle producers. Knowing the magnitude and mechanisms of pesticide resistance in southern cattle ticks present close to the quarantine zone allows USDA APHIS VS personnel to understand the risk that resistance poses to the eradication program and choose the correct chemical needed to quickly and efficiently eradicate outbreak populations of ticks within the country. This is the first documented resistance in Mexico along the northern part of the U.S. quarantine zone.

Technical Abstract: Boophilus microplus, collected in Coahuila, Mexico were determined to be resistant to permethrin. Discriminating concentration (DC) tests at the LC99 and 2X the LC99 of susceptible ticks produced 0 and 0.5% mortality, respectively for permethrin. However, measured mortalities for coumaphos and amitraz acaricides were within the expected ranges. PCR analysis of this strain detected a 99% frequency of homozygous resistant individuals in this strain. Key words: Rhipicephalus (Boophilus) microplus, pesticide resistance, southern cattle tick, acaricide, permethrin