Acaricide resistance of Rhipicephalus (Boophilus) decoloratus (Acari: Ixodidae) on commercial farms in South Africa: filling a gap in historical data.

In South Africa, acaricides are widely used for tick control but very few reports are available on resistance development of Rhipicephalus (Boophilus) decoloratus Koch to chemical control on commercial farming systems in Africa, south of the Sahara. Resistance to different acaricide classes reported over the years was mostly from localised communal farming systems. This report addresses the lack of available information on resistance development by reviewing results found during a National Tick Resistance Survey carried out from 1998 to 2001, laying the foundation for more recent research on resistance development, and the evolution of resistance over the years. One hundred and eighty R. decoloratus populations were randomly collected from commercial farming systems, covering most of the provinces of South Africa. Larval immersion tests were used to determine phenotypic resistance for each tick population and 6.6% of the populations tested were found to be resistant to amitraz, 35.5% to cypermethrin, and 36.1% to chlorfenvinphos. Multi-resistance to all three acaricides was found in 1.2% of populations and a further 25.8% of the populations were resistant to two acaricides. The detection of resistance of Rhipicephalus (Boophilus) species to currently used or new acaricides is an essential tool in resistance management. The acaricides tested for the resistance of R. decoloratus during the survey are currently still in use in South Africa and these historical results, never published before, can be valuable and can act as reference data to determine the evolution of resistance development to acaricides in more recent studies.