Characterization and establishment of a reference deltamethrin and cypermethrin resistant tick line (IVRI-IV) of Rhipicephalus (Boophilus) microplus.

The problem of ticks and tick borne diseases is a global threat and growing reports of resistance to commonly used insecticides further aggravated the condition and demands for country specific resistance monitoring tools and possible solutions of the problem. Establishment of standard reference is prerequisite for development of monitoring tools. For studying possible role of different mechanisms involved in development of resistance in Rhipicephalus (Boophilus) microplus population and to develop newer drug to manage the problem of resistance, a deltamethrin exposed and selected tick colony, referred to as IVRI-IV, was characterized using reference susceptible IVRI-I tick line as control. The RF values of IVRI-IV ticks against deltamethrin, cypermethrin and diazinon were determined as 194.0, 26.6, 2.86, respectively, against adults. The esterase enzyme ratios of 2.60 and 5.83 was observed using α-naphthyl and ß-naphthyl acetate while glutathione S-transferase (GST) ratio was 3.77. Comparative analysis of IVRI-I and IVRI-IV carboxylesterase gene sequences revealed 13 synonymous and 5 non synonymous mutations, reported for the first time. The C190A mutation in the domain II S4-5 linker region of sodium channel gene leading to leucine to isoleucine (L64I) amino acid substitution was also detected in the IVRI-IV population. In the present study, monitorable indicators for the maintenance of the reference IVRI-IV colony, the first established deltamethrin and cypermethrin resistant tick line of India, were identified.