author(s)
Kumar SS, Rayulu VC, Rao KS and Kumar NV

abstract
The present study was conducted during the period from January to July, 2015 to determine the status of resistance in Rhipicephalus (Boophilus) microplus ticks infesting cattle in different parts of Andhra Pradesh to commonly used acaricides viz., deltamethrin, cypermethrin and amitraz. Larval Packet Test (LPT) bioassay revealed the highest LC₅₀ values for both deltamethrin and cypermethrin against R. (B.) microplus ticks collected from Chittoor (40.05 ppm and 88.68 ppm) followed by Prakasam (12.59 ppm and 36.58 ppm) and YSR Kadapa (8.10 ppm and 30.82 ppm), respectively. The tick populations of Chittoor showed significantly (P<0.05) higher resistance to deltamethrin (RF=8.78; RL=II) and cypermethrin (RF=7.04; RL=II) followed by Prakasam (RF=2.76; RL=I); (RF=2.90; RL=I) and YSR Kadapa (RF=1.78; RL=I); (RF=2.45; RL=I), respectively. The tick populations in Anantapur, Krishna and Vizianagaram were found to be susceptible (RL S = RF<1.1) to synthetic pyrethroids. Modified LPT indicated that the R. (B.) microplus ticks collected from different parts of Andhra Pradesh were totally susceptible to amitraz. LC₅₀ values for various tested populations of R. (B.) microplus for amitraz were recorded in between 76.02 and 84.94 ppm against 73.97 ppm of reference population.