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 estcrases 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 acetyleholinesterase (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 clays 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 clays 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%).