Progression of deltamethrin resistance in Rhipicephalus microplus populations on communal farms of South Africa.

This study was conducted to assess the progression of deltamethrin resistance in Rhipicephalus (B.) microplus populations over a 5-year period, from 2019 to 2023, on selected communal farms in the Eastern Cape Province, South Africa. Ticks were collected from three communal farms with a documented history of deltamethrin resistance in R. (B.) microplus populations in 2019. The sampled tick populations were tested for resistance using the adult immersion test (AIT). The data generated from the AIT indicated deltamethrin resistance, with oviposition inhibition percentages ≤ 95% at both the manufacturer's recommended dose and twice the recommended dose. These findings confirm the establishment of deltamethrin resistance in R. (B.) microplus populations on the communal farms within the KSD local municipality, following over a decade of frequent and continuous use of this acaricide. Ticks on cattle, along with their control and acaricide resistance in tick populations, pose a significant threat to livestock production on communal farms in South Africa.