Resistance status of ticks (Acari; Ixodidae) to amitraz and cypermethrin acaricides in Isoka District, Zambia.

This study was designed to obtain data on the farmer's approach to tick control and to determine whether Rhipicephalus appendiculatus Neuman, Amblyomma variegatum (Fabricius), and Rhipicephalus (Boophilus) microplus (Canestrini) were resistant to amitraz and cypermethrin acaricides, in Isoka District, Zambia. Prevailing tick control practices were documented by administering a semi-structured questionnaire to 80 randomly selected smallholder livestock farmers from four agricultural camps (Longwe, Kantenshya, Kapililonga, and Ndeke) in Isoka District. Modified larval packet test (LPT) bioassay experiments were used to determine the resistance status of the common tick species against amitraz and cypermethrin acaricides. Fifty percent of respondents practiced chemical tick control with amitraz (27 %) and cypermethrin (23 %) being the acaricides in use, and were applied with knapsack sprayers. Less than 3 l of spray wash per animal was used which was considerably lower than the recommended delivery rate of 10 l of spray wash per animal. No significant susceptibility change to amitraz at 95 % confidence level was observed in R. appendiculatus and A. variegatum against amitraz. However, a significant change in the susceptibility of R. (Bo.) microplus tested with amitraz was detected at 95 % confidence. The test population had a lower susceptibility (LD50 0.014 %; LD90 0.023 %) than the reference population (LD50 0.013 %; LD90 0.020 %). The results indicated that resistance to amitraz was developing in R. (Bo.) microplus. For cypermethrin, no significant susceptibility change at 95 % confidence was observed in any of the three species and thus resistance to this chemical was not observed.