Acaricide resistance patterns in one-host Rhipicephalus spp. at communal dip tanks and neighbouring commercial farms in the KwaZulu-Natal Midlands

Abstract

This project was conducted in order to ascertain the presence or absence of acaricide resistance in ticks in an area of KwaZulu-Natal (KZN) where tick-borne diseases pose a real and dire threat to communal and commercial livestock. The results of this study will assist farmers and state veterinarians in their tick control strategies and aid in the battle against stock losses due to ticks and tick-borne diseases. The aim of the project was to collect one-host Rhipicephalus spp. (blue ticks) from cattle presented at communal dip tanks and from cattle on commercial dairy and/or beef farms to test for the presence of acaricide resistance. The ticks were identified as either R. microplus or R. decoloratus, then the engorged female ticks were incubated and the hatched larvae subjected to the Shaw Larval Immersion test (SLIT). The Shaw Larval Immersion test was developed in 1966 by RD Shaw (Shaw, 1966) to determine the spectrum of acaricide resistance in tick populations. The three acaricides selected for the laboratory bio-assay are included in the classes of topical acaracides most frequently used in KZN, namely amidines, organophosphors and pyrethroids. Both tick species were present in the study area and two commercial farms showed a mixed population of both tick species. All fifteen populations of ticks tested in this study showed resistance to at least one class of acaricide, and four of the 15 (26%) showed resistance to two classes of acaricides. 80% of the tick samples tested was resistant to cypermethrin, a synthetic pyrethroid. It can be concluded from this study that: 1. acaricide resistance is present in one-host Rhipicephalus spp. in the KwaZulu-Natal Midlands and this poses a real and significant threat to tick control efforts in this region of KwaZulu-Natal, 2. resistance to pyrethroids is developing at a faster rate than other acaricides and, 3. both blue tick species were identified in the study area however only one or the other species was represented at almost all of the 15 sites sampled. The exceptions were two commercial farms, where both R. decoloratus and R. microplus were identified in a mixed population.