Synthetic pyrethroid resistance in Rhipicephalus microplus associated with metabolic detoxification mechanism

Larval packet test was utilized for detection of resistance against commonly used synthetic pyrethroid acaricides viz. cypermethrin and deltamethrin in cattle tick, Rhipicephalus microplus (R. microplus) populations from various districts of Punjab, India. The values for the lethal concentrations at 50% mortality (LC50) for cypermethrin and deltamethrin were estimated by probit analysis and the Resistance Factor (RF) was calculated. The RF values for R. microplus isolates against cypermethrin ranged from 0.07 to 4.31 indicating susceptibility in five field isolates of western Punjab and level I resistance status in the other three isolates collected from Muktsar, Barnala and Bathinda districts. Similarly, the RF values against deltamethrin ranged from 0.27 to 24.35 with susceptibility in only single isolate from the Bathinda district, level I resistance status in three isolates (Sangrur, Moga and Mansa) and level II status in other four isolates (Ferozepur, Barnala, Muktsar and Fazilka). The α- and β-esterase enzyme activity in the field isolates were estimated as 3.496±0.24 - 5.346±0.75 and 1.801±0.14 - 3.101±0.27 µmol/min/mg protein, respectively and glutathione-S-transferase (GST) enzyme activity was recorded as 0.0265±0.0007 - 0.0300±0.0015 mmol/mg/min in various field isolates. A strong correlation was recorded between enzyme ratios of α-esterase and GST enzymes of the R. microplus field isolates and the resistance factor values against deltamethrin which may be playing a major role in developing resistance.