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Evaluation of acaricide resistance mechanisms in field populations of Rhipicephalus (Boophilus) microplus collected from India

ABSTRACT A study was conducted to monitor the status of deltamethrin resistance in field populations of Rhipicephalus (Boophilus) microplus from different geographical locations of Uttarakhand state in northern India and mechanisms involved therein. The highest 50% lethal concentration (LC50) was recorded for the Kashipur population of ticks [0.0175%; resistance factor (RF) = 34.26] followed by Nagla (0.00273%; RF 5.35), Dehradun (0.00266%; RF 5.21), Pantnagar (0.002402%; RF 4.71), Almora (0.00164%; RF 3.21), and the lowest was recorded for the ticks from New Tehri (0.00104%; RF 2.04) when compared with the reference susceptible Pithoragarh strain (LC50 0.00051%; RF 1.0). The in vitro laboratory evaluation revealed three tick populations to have deltamethrin-resistant phenotypes (RF > 5); two populations to be tolerant (RF 3–5) and one population to have susceptible phenotypes (RF < 3). Synergism studies revealed the likely involvement of monoxygenases (minor role) and esterases in the resistant phenotypes of Nagla ticks; the involvement of esterases in imparting resistance in Dehradun ticks; and no role for the metabolic detoxification mechanism in Kashipur ticks. This is the first report from India describing the development of deltamethrin resistance in R. microplus. The results suggest that integrated management of ticks including strategic and judicious use of acaricides, is required before deltamethrin resistance becomes established in this part of the country and spreads to other areas.