Current profile of phenotypic pyrethroid resistance in Rhipicephalus microplus (Acari: Ixodidae) populations sampled from Marathwada region of Maharashtra state, India

Abstract

This study examined the pattern of resistance to widely applied synthetic pyrethroids i.e. cypermethrin and deltamethrin, against larvae of Rhipicephalus microplus ticks sampled from Marathwada region in Maharashtra, India. The study also examined the role of α and β-esterase's and glutathione-S-transferase (GST) in resistance development.All eight R. microplus isolates tested were resistant to deltamethrin (RL IV), having RR 50 values from 6.88 to 131.26.LPT analysis exhibited the resistance level II deltamethrin resistance in Beed and Hingoli, III in Dharashiv, and IV in Sambhajinagar, Parbhani, Latur, Jalna, and Nanded isolates. The LIT analysis showed that Dharashiv eld isolates had the lowest LC 50 value of 229.09 ppm against cypermethrin, while Sambhajinagar eld isolates had the highest at 489.78 ppm. The RR 50 ranged from 1145.45 to 2448.9. Seven isolates were level I resistant to cypermethrin while the Jalna isolate was level II resistant. In larvae treated with deltamethrin and cypermethrin, the activity of α and β-esterase enzymes increased signi cantly compared to control groups. The enzyme ratios in treated larvae ranged from 0.7533 to 1.7023 for α-esterase and 0.7434 to 3.2054 for β-esterase. The Hingoli isolate treated with cypermethrin exhibited the highest α-esterase activity (903.261), whereas, Sambhajinagar isolate had the highest GST enzyme ratio (2.8224) after deltamethrin exposure. When exposed to cypermethrin, the Hingoli isolate showed the highest GST enzyme ratio, 2.0832.