Effect of an organophosphate,pirimiphos-methyl,on esterases of different developmental stages of stored grain pest red flour beetle,Tribolium castaneum (Herbst.) - Spectrophotometric analysis

The effect of sub-lethal doses of an organophosphorus insecticide,pirimiphos-methyl,has been described on esterases of tribolium castaneum collected from stored grain godown and compared with those of insecticide resistant (ctc-12) and susceptible (fss-ii) strains to establish insecticide resistance of the pest and hence suggested alternate control measures. the multiple forms of esterases activities were determined biochemically,using spectrophotometer. after treatment with pirimiphos-methyl the soluble proteins of 4th instar larvae of pak strain decreased (30%),while that of other strains increased. the other stages of the three strains did not show any significant change after insecticide treatment. the pirimiphos-methyl treatment significantly decreased the carboxylesterase (ce) activity in all the developmental stages (4th and 6th instar larvae,newly emerged and 15 days old beetles) of pak strain (56,29,76 and 66%),fss-ii strain (81,75,64 and 27%) and ctc-12 strain (61,58,51 and 48%). the acetylcholinesterase (ache) activity decreased significantly with the treatment in all stages of the three strains. the cholinesterase (che) activity increased (65,59 and 37%) only in the 4th and 6th instar larvae and 15 days old adult beetles of pak strain,while it decreased (31%) in the newly emerged adults. the various developmental stages in fss-ii and ctc-12 strain,however showed opposite response. che activity of 15 days old beetles increase (21 and 80%),while that other stages decrease after treatment with pirimiphos-methyl. the arylesterase (ae) activity in all the three strains decreased from the 4 th instar larvae to 15 days old adults after pirimiphos-methyl treatment. the total esterase (te) activity was significantly inhibited in the four stages of the three strains (pak 54,48,69 and 59%; fss-ii 80,69,62 and 6%: ctc-12 73,62,67 and 71%). copyright 2012 zoological society of pakistan.