In vitro susceptibility study of Amblyomma cohaerens and Rhipicepalus (Boophilus) decoloratus tick species to amitraz 12.5 % and diazinon 60 % acaricides in Jimma town, Ethiopia.

The study was conducted to evaluate the in vitro efficacy of amitraz 12.5 % and diazinon 60 % against Amblyomma cohaerens and Rhipicephalus (Boophilus) decoloratus, and also to assess acaricide resistance using the Adult Immersion Test (AIT) in Jimma town, Oromia region, southwest Ethiopia. A total of 180 engorged adult female ticks of the two species (90 A. cohaerens and 90 R. decoloratus) were collected from local and crossbred cattle managed under extensive and semi-intensive systems. The ticks were immersed in amitraz 12.5 % and diazinon 60 % at field-recommended concentrations, and in distilled water for the control groups, for two minutes. Afterward, they were placed in an incubator at 27°C and 85 % RH for seven days. The oviposition responses of A. cohaerens and R. decoloratus were monitored regularly. The efficacy of each acaricide was assessed by comparing the mean egg mass laid by treated and untreated tick groups. The study results showed that ticks treated with amitraz 12.5 % died and did not lay eggs, while some ticks treated with diazinon 60 % survived and laid eggs after a seven-day incubation period. There was a significant difference (p < 0.05) between the two acaricides in controlling egg-laying in both species of ticks. The ticks in the control group that were treated with water survived and laid eggs. Amitraz 12.5 % at the field-recommended concentration achieved 100 % control, whereas diazinon 60 % achieved 91.3 % control. The study shows that both amitraz 12.5 % and diazinon 60 % significantly reduced egg laying in A. cohaerens and R. decoloratus ticks. The results also demonstrate that amitraz 12.5 % is more effective in controlling ticks and that there is a sign of emerging resistance of ticks to diazinon 60 %.