Prevalence and potential risk factors for pyrethroids resistance in Boophilus microplus ticks on milk farms in Santa Cruz Department, Bolivia

Abstract

A cross-sectional study was done of the association between risk factors and the prevalence of Boophilus microplus ticks resistant to synthetic pyrethroids (SP) in Santa Cruz Department, Bolivia. Eighty-three dairy farms were randomly selected and a sample of 10 to 50 engorged female B. microplus ticks collected at each. Tick progeny were produced to test for SP resistance. The Larval Packet Test with a discriminating dose was done to detect flumethrin (0.01%), deltamethrin (0.09%) and cypermethrin (0.05%) resistance in the ticks. Two reference strains with a specific response type (previously reported in Australia and Mexico) were used: Marmor (resistance to deltamethrin and cypermethrin) and Parkhurst (resistance to flumethrin, deltamethrin and cypermethrin). A third response type of resistance to deltamethrin was identified for the first time in this study and called the Santa Cruz type. Overall prevalence of pyrethroids-resistant ticks among the sampled farms was 92.7%. Flumethrin resistance was observed at 42 % of the farms, deltamethrin resistance at 88.0 % and cypermethrin resistance at 75.9 %. Response type prevalence was: Marmor 32.5 %, Parkhurst 38.5 %, and Santa Cruz 14.4 %. The risk factor significantly associated with occurrence of the Marmor-type response was grazing in public areas, and that significantly associated with occurrence of the Parkhurst-type response was grazing on producer property. The high prevalence of SP-resistant B. microplus tick populations on dairy farms in Santa Cruz Department poses a problem for production, and grazing practices is a risk factor for the presence of the Marmor- and Parkhurst-type responses.