Prevalence and potential risk factors for amitraz resistance in Boophilus microplus ticks in cattle farms in the State of Yucatan, Mexico.

Southern cattle tick, Boophilus microplus, control in the Mexican tropics is based on the application by spray, dip or pour-on of acaricides. In Mexico the first report of ticks resistant to amitraz was reported in 2002. Amitraz resistance affecting the cattle industry of Yucatan State, Mexico, has not been investigated. A cross-sectional study was carried out in order to investigate the possible association between management risk factors and the prevalence of B. microplus ticks resistant to amitraz in Yucatan, Mexico. Ninety-eight cattle farms were randomly selected and a sample of 20-30 engorged B. microplus females was collected from at least 10 cattle from each farm. Collected ticks were taken to the laboratory where the larval progeny were obtained. The modified larval immersion test was used to detect ticks resistant to amitraz. A discriminating dose of 0.0002% amitraz was used. A questionnaire was applied on each collaborating farm. For the statistical analysis a 2x2 contingency table was used to identify potential risk factors. The prevalence of farms with B. microplus resistant to amitraz was 19.40%. However, even though tick resistance to amitraz is a present problem there was no evidence that it was associated with the risk factors analyzed in this survey.