
%0 Journal Article
%A Schuntner, CA 
%A Thompson, PG 
%T Mechanisms of Resistance to Bromophos-ethyl in Two Strains of the Cattle Tick Boophilus microplus
%J Australian Journal of Biological Sciences
%D 1978/08/01
%V 31
%N 4
%P 317-326
%K 
%R https://doi.org/10.1071/BI9780317
%U https://www.publish.csiro.au/paper/BI9780317 
%X B. micro plus larvae of the organophosphorus-resistant Biarra and Mt Alford strains were respectively 8 x and 35 x resistant to bromophos-ethyl compared with larvae of the standard organophosphorussusceptible Yeerongpilly strain. Both resistant strains had acetylcholinesterase with decreased sensitivity to inhibition by the oxon of bromophos-ethyl in vitro; this was the only resistance mechanism apparent in the Biarra strain but Mt Alford larvae were protected additionally by increased metabolism of the oxon in vivo to water-soluble products. Total degradation rates for the parent chemical were similar in all strains and relatively slow. Both bromophos-ethyl and its oxon were potent inhibitors of mixed-function oxidase in vivo and it seemed that the slow oxidative metabolism of bromophos-ethyl (the major pathway) could be attributed to substrate and/or product inhibition. No phenolic metabolites were detected and the major water-soluble metabolite was identified electrophoretically as 2,5-dichlorophenyl-o-ethyl phosphate. Some debrominated oxon was detected in all samples of larvae after dosage with bromophos-ethyl or with its oxon, indicating that oxidation of bromophos-ethyl to the oxon, debromination of the oxon followed by deethylation was a major degradative sequence. 
