Comparative efficacy of two synthetic pyrethroids against Rhipicephalus (Boophilus) microplus

Abstract

A study was conducted to estimate the efficacy of market available formulations of two synthetic pyrethroids namely cypermethrin and fenvalerate. Fully engorged females of Rhipicephalus (Boophilus) microplus were collected from different locations of North India. Larval Packet Test (LPT) was conducted on 14 to 21 days old larvae of these tick samples. Ticks reared in the Department of Veterinary Parasitology, GB Pant University of Agriculture & Technology were used as reference susceptible population. Different dilutions of cypermethrin and fenvalerate were prepared in 2:1 solution of trichloroethylene and olive oil as per FAO recommendation. The same solution was used as control. LPT bioassay revealed tick population of Dehradun to be least susceptible, with highest LC50 values against both cypermethrin (0.03459% Active Ingredient (AI)) and fenvalerate (0.89802% AI). LC50 value of cypermethrin was lowest for Bheemtal (0.0006% AI) and for fenvalerate it was for Pantnagar (0.01817% AI). Four of the tick populations were resistant to cypermethrin (Resistance Factor (RF) > 5) and only tick populations of Dehradun was resistant to fenvalerate. The above study indicates that there is a rise in resistance against the two commonly used synthetic pyrethroids in tick populations of these regions and there is a variation in efficacies of the two acaricides. Thus to prevent the\n emergence of resistant tick populations in this region, acaricides must be used judiciously and there should be frequent monitoring of efficacy of these acaricides.