A study was conducted (November 2012) on the communal dipping system in Mnisi, Mpumalanga Province of South Africa to detect levels of blue tick resistance to commonly used acaricides. The larvae obtained from engorged females of the one host tick Rhipicephalus (B). microplus from twelve communal dipping areas were tested against various concentrations of amitraz, chlorfenvinphos and cypermethrin using the Shaw Larval Immersion Test method. Only R. (B). microplus ticks were identified from all sample areas, indicating a displacement of the indigenous R. (B). decoloratus tick in this area. Resistance testing using the Shaw Larval Immersion Test showed that no resistance to chlorfenvinphos was detected at any of the dip tanks, which was in keeping with the absence of known use of this product in the area. An important finding was the rapid development of resistance to the pyrethroids, which had only been in use for four months prior to conducting the study. Only one area (Hlalakane) yielded a R(B).spp population that was wholly susceptible to all three compounds. Resistance to amitraz was variable, with half (six out of 12) of the dip tanks comprising susceptible R(B).spp populations and two dip tanks with emerging resistance to amitraz.
Possible risk factors which caused the resistance problems are discussed and acaricide management strategies recommended.