The distribution of Rhipicephalus (Boophilus) microplus and Rhipicephalus (Boophilus) decoloratus on a farm in the Eastern Cape Province, South Africa
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The Asiatic blue tick, Rhipicephalus (Boophilus) microplus is an invasive tick species which was introduced to South Africa in 1896. Reports dating back to the early 1900s state that the displacement of the African blue tick, Rhipicephalus (Boophilus) decoloratus had occurred within the Cape region. Rhipicephalus (Boophilus) microplus has the ability to adapt to new environments, is a vector of disease and has been reported to have developed resistance towards most available acaricides over a short period of time. The control of this species has become a major challenge to producers all over the world. The Eastern Cape Province accounts for the highest percentage of cattle production in South Africa. To date there is comprehensive data available on the tick distribution in South Africa however, many of the studies conducted in the Eastern Cape were completed on communal farms and the acaricide resistance status of these localities remains unknown as the majority of the studies have not included this aspect. The aim of this study was to provide information regarding the blue cattle tick composition, distribution and acaricide resistance status of a commercial cattle farm near Grahamstown in the Eastern Cape. Engorged adult females were collected directly from the cattle and questing larvae were collected from the vegetation through drag sampling technique. All ticks and larvae were identified up to species level with the aid of morphological characteristics. Polymerase Chain Reactions-(PCR), was used to complement the morphological identification of the larvae as this life stage can be difficult to identify due to under developed features. A total of seven tick species; Amblyomma hebraeum, Haemaphysalis elliptica, Hyalomma truncatum, Ixodes pilosus, Rhipicephalus (Boophilus) decoloratus, Rhipicephalus (Boophilus) microplus and Rhipicephalus evertsi evertsi, were identified on the farm. Rhipicephalus (Boophilus) decoloratus was found to be the predominant tick and blue tick species on the farm while R. (B.) microplus was found to be present on the farm in various different camps over the study period, however, not in large numbers. The movement of a selected herd was tracked over a year period and provided a rough picture of how R. (B.) microplus was being spread over the farm. The relationship between temperature and humidity on the number of questing larvae collected was found to be inconclusive presenting a weak correlation between both temperature and larvae collected as well as relative humidity and larval numbers questing. The Shaw Larval Immersion test (SLIT), was conducted to establish resistance profiles for the various camps where tick collections were conducted. The chemicals which were tested included: Amitraz (Amidine), Chlrofenvinphos (Organophosphate) and Cypermethrin (Pyrethroid). Results were obtained for R. (B.) decoloratus as R. (B.) microplus was not collected in large enough numbers for testing. The results show that there is a definite shift towards the development and emergence of resistance on the farm towards Amidine based acaricides. Synthetic Pyrethroids and Organophosphates showed fewer extreme results. There was a definite variation between different camps on the farm. Multi-host tick resistance was also tested and it was found that both the three-host Amblyomma hebraeum and the two-host Rhipicephalus evertsi evertsi were susceptible to all the chemical groups tested. The results of this study provide a foundation for tracking the invasion of Rhipicephalus (Boophilus) microplus as well as aiding the producer in the management of acaricide resistance on the farm.