Histochemical Localization of Esterases in the Integument of the Female Boophilus microplus (Acari: Ixodidae) Tick
ABSTRACT The cattle tick Boophilus microplus (Canestrini) is one of the most important ectoparasites affecting tropical cattle with worldwide distribution. Application of organophosphate compounds (OP) is extensively used as a tick control method. However, the appearance of ticks resistant to the OP decreases the therapeutic efficacy of such compounds. Esterases have been implicated as potential biochemical mechanisms for detoxification in B. microplus larvae. We found increased esterase activity in the inner layers of the integument of OP resistant adult female B. microplus ticks as compared with the OP susceptible ticks. We discuss the potential role of these enzymes during acaricide metabolism and propose future research.
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ABSTRACT: The cattle tick Boophilus microplus causes significant economic losses in cattle in the tropical areas of Central and South America. Acaricides are widely used to control tick infestations, with the consequent selection of tolerant and resistant subpopulations. Detoxifying enzymes, and esterases in particular, have been associated with organophosphate resistance in Mexican isolates of B. microplus ticks. Here, we present results of the biochemical detection of esterases and oxidases in 20 isolates of larvae and adult ticks and the effect of esterase and oxidase inhibitors on larvae and adult stages of the tick. Our results indicate the presence of significant differences both in vivo and in vitro between esterase and oxidase activities of OP-susceptible and OP-resistant isolates, even when samples were collected in the same area. The importance of such differences in regionalized integrated pest management and in the US Tick Eradication Program is discussed.Enperimental and Applied Acarology 01/2002; 28(1-4):265-71. DOI:10.1023/A:1025371105437 · 1.82 Impact Factor
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ABSTRACT: Chemical control based on the use of pyrethroid and organophosphate compounds has selected resistant genotypes in populations of Rhipicephalus (Boophilus) microplus. Point mutations in esterase-encoding genes represent one of the main resistance mechanisms in this species. In this study, the PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) technique was used to investigate the presence of mutations in a fragment of a putative carboxylesterase in a population of ticks with a history of resistance. The digestion of a fragment of 372 pb with EcoRI revealed three genotypes: W, H and M, observed in different frequencies. The homozygous wild-type genotype (W) was detected only in sensitive strains, with high frequency. The heterozygous genotype (H) was observed in all the strains, albeit with higher frequency in the strains with a moderate resistance, while the homozygous mutant genotype (M) was found only in the moderate resistant strain and resistant strains, with higher frequency in the resistant strains. A comparison of the sequences indicated the presence of other mutations, besides EcoRI polymorphism in the moderate resistant and resistant strains. Also found was the presence of stop codons generating truncated proteins in the sensitive and moderate resistant strains. A domain analysis revealed the presence of additional domains in the resistant strain. These findings suggest that different point mutations, as well as the influence of post-translational modification mechanisms, are altering the activity of the translated proteins and may be associated with resistance.Veterinary Parasitology 10/2007; 148(3-4):301-9. DOI:10.1016/j.vetpar.2007.06.016 · 2.55 Impact Factor