General esterase activity variation in the cattle tick Boophilus microplus and its relationship with organophosphate resistance

Abstract

Increased esterase activity in arthropods is considered as an important biochemical marker of pesticide resistance. In Boophilus microplus, esterases have been associated with resistance to both organophosphate and pyrethroid families. The purpose of this study was to analyze ixodicide resistance in five B. microplus strains with different levels of susceptibility as measured by esterase activity and its correlation with resistance indexes (RI). Toxicological analysis was performed using the larval package bioassay with one discriminating dose equivalent to 2X the LD99 as determined by the Probit analysis, from which the RI for each strain was estimated. Larval protein extracts from each of the five strains were obtained by homogenizing 100 mg of 10-day-old larvae in 2 ml of phosphate buffer solution. The larval protein homogenates were spectrophotometrically analyzed for esterase detection. Specific esterase activity showed a significant (P<0.05) correlation with the RI of chlorfenvinphos (r=0.80), but not with those of coumaphos (r=0.70) or diazinon (r=0.47). It was concluded that esterase spectrophotometric detection is a resistance marker for chlorfenvinphos B. microplus resistance, and it can be easily adapted to a microplate, and proposed as a fastest, easiest and sensitive method when compared with the traditional larval package bioassay.