Ixodid ticks transmit a number of diseases to humans and animals. Recent researches revealed that ticks have developed resistance against a range of acaricides. Therefore, for an optimal control, mechanisms involved in the insecticide resistance should be studied in this group of ticks.Adult ticks were collected from different locality and bioassay test were conducted using the larva pocket test. The results were compared to those of a susceptible strain. Biochemical assays of esterases, monooxigenases, glutathione S-transferase (GST) and acetylcholine esterase levels were undertaken on larva of Boophilus decoloratus from different locality.All the species of ticks collected from Aligarh city and suburbs were found resistant level I against organophosphates. The activity of esterase was found 1.24-1.86 times higher in city strain of B. decoloratus. The increase in esterase in field strain (City) was about 1.14-1.76 times more in B. decoloratus, than the susceptible strain (village). The GST values were found 1.28-2.59 times higher in the field strain of B. decoloratus as compared to control.The maximum values content of p450 were 1.28-2.59 times higher in B. decoloratus than village strains and the inhibition values in the field population were found comparatively less than village population.The Resistance ratio values and also the activity of all enzyme groups in field strains were significantly different from those of the susceptible strain. Although organophosphate can still be theoretically used in controlling Boophilus decoloratus it is wise to put the pesticide resistance management strategies in place to avoid or postpone further development of organophosphate resistance.

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