Detection of amitraz resistance in Rhipicephalus (Boophilus) microplus from North Gujarat, India

Amitraz has become one of the most extensively used chemical acaricide for control of cattle tick due to development of resistance against most of the organophosphates and synthetic pyrethroid acaricides. The resistance status of amitraz was evaluated against Rhipicephalus (Boophilus) microplus collected from Banaskantha district, Gujarat, India by adult immersion test (AIT). The different concentrations of amitraz utilized in the AIT were 125, 250, 500, 750 and 1,000 ppm. The adult female ticks showed an upward trend in the mortality percentage with increase in drug concentration. The regression graph of probit mortality of ticks plotted against log values of progressively increasing concentrations of amitraz was utilized for the determination of slope of mortality which was 1.868 ± 0.2068. The lethal concentration (LC95) was calculated as 3098.2 ppm and the RF was 24.78 which indicated level II resistance status. The dose response curves for egg masses, reproductive index and inhibition of oviposition of R. (B.) microplus were also validated and the slope was -0.5165 ± 0.08287, -0.1328 ± 0.04472 and 24.22 ± 8.160, respectively. The current study appears to be the pioneer report of amitraz resistance in R. (B.) microplus from India and the data generated could be of immense help to develop effective control strategies against ticks.