LAUSR

Hyalomma dromedarii ticks collected from a camel herd of Hanumangarh district in the Rajasthan State of India were subjected to FAO recommended adult immersion test with discriminating dose (AIT-DD) against amitraz (formamidines), deltamethrin (synthetic pyrethroids) and coumaphos (organophosphate). The country-specific data generated using the IVRI-I line (deltamethrin (59.2 ppm), coumaphos (262 ppm) and amitraz (975.40 ppm)) was taken as discriminating dose for concerned acaricide since the reference susceptible H. dromedarii ticks line is not maintained anywhere in world. Standard FAO protocol for the rapid detection of acaricide resistance was followed. The percent resistance against deltamethrin, coumaphos and amitraz were found to be 26.67%, 46.67% and 0% respectively. Results revealed a high susceptibility of these ticks against amitraz, resulting in 100% mortality at discriminating concentration. Esterase characterization using Native PAGE of Hyalomma dromedarii homogenate reveals a total of 7 esterase bands, viz. Est-1 h-5 h, Est-7 h and Est-8 h in larva and only 5 esterase bands viz. Est-1 h, Est-3 h-4 h, Est-6 h and Est-7 h in adult. Inhibition assay using inhibitors (copper sulphate, p-chloromercuribenzoate, eserine sulphate, phenylmethylsulfonylfluoride) against esterase of H. dromedarii ticks confirms the presence of serine residues in their active site and provide evidence for the presence of Est-7 and Est-8 in larvae as acetylcholinesterases (AChEs) in larvae. It is the first attempt of biochemical characterization of esterases present in H. dromedarii ticks and could be in future related with development of resistance against organophosphates and synthetic pyrethroids compounds. The high susceptibility status to formamidines drugs may be attributed to low selection pressure as they are still preferred next to synthetic pyrethroids in veterinary practices. It also indicates an alternative tick control measure needs to be adopted in camels to extenuate the development of acaricide resistance.