Biossay of acaricide resistance on three common cattle tick species at Holotta, Central Ethiopia

Bioassay of acaricide resistance on three common cattle ticks was carried o ut on four farms in Holotta area, Central Ethiopia, using a standardized FA O Acaricide Resistance Test Methods. Larval progeny of Boophilus decoloratu s, Rhipicephalus e. evertsi and Amblyomma variegatum were subjected to larv al packet test (LPT) employing four different acaricides (Dieldrine, Diazin on, Chlorfenvinphos and Coumaphos) each with five concentration levels. Str ains of Boophilus decoloratus, Rhipicephalus e. evertsi, originated from an area where there is no tradition of acaricide application for tick control , were used as reference ticks. Extremely high susceptibility of reference tick strains was confirmed to al l the tested acaricides. Statistical analysis of pooled mean mortality rate s revealed that B. decoloratus strains were found resistant to Dieldrine an d Diazinon in all studied farms; and to Chlorfenvinphos and Coumaphos only at the Sadamo farm. In addition, strains of R. e. evertsi from the research station farm revealed a slight degree of resistance to Coumaphos. A. varie gatum strains from all farms showed high degree of susceptibility to all te sted acaricides. The finding of organophosphate resistance is the first rep ort of its kind in Ethiopia. Extensive uses of acaricides like BHC and Bacd ip; irregular spraying, failure to maintain adequate lethal concentrations and other managerial constrains hampering the successful use of acaricides are anticipated causes of the emerging acaricide resistance in the study ar ea. Pertinent recommendations were made to alleviate the existing problem i n the study area as well as in other affected regions in the country.