Biochemical detection of esterases in the adult female integument of organophosphate-resistant Boophilus microplus (Acari: Ixodidae)

Esterase activity was present in the integument of adult female Boophilus microplus (Canestrini) ticks that are resistant to organophosphates (OP). Three esterases were purified from adult integument, which hydrolyze the substrates p-nitrophenylacetate and beta-naphthyl acetate after comparison of OP-resistant strain and an OP-susceptible strains. The esterases purified by ion-exchange chromatography were characterized using different esterase inhibitors; eserine sulfate, diethyl p-nitrophenyl phosphate (paraoxon), para-hydroxyl-mercuribenzoate (pHMB), and diisopropylphosphofluoridate (DFP). All of the esterases had a molecular mass of 64 Kd (PAGE), but were characterized based on the esterase inhibitor effects as a B-esterase with beta-naphthyl acetate affinity, a carboxylesterase with beta-naphthyl acetate and p-nitrophenyl acetate affinity, and one A-Esterase (nonspecific esterase) with p-nitrophenyl acetate affinity. The described esterases are an important detoxification mechanism in B. microplus ticks at the integument. We describe also a microplate biochemical assay for the detection of esterase activity in the tick integument, potentially a useful tool to detect esterase-mediated OP resistance in B. microplus ticks.