An investigation was performed to determine the possible role of detoxification metabolism in resistant strains of
Tetranychus urticea Koch.Adult females were subjected to selection pressure through 40 generations by LC50's and
LC90's of Vertimec (Avermectines), Cypermethrin (Pyrethroids), Methomyl (Carbamates) and Malathion (O.P), were
(41.308, 42.021, 44.881, and 49.265 folds) and (49.815 ,55.411 ,63.972 ,and 90.00 folds), respectively, whereas RRS
slopes ranged from 0.884 to 1.395 folds. Comparative assay with esterases (EST) and mixed function oxidases(MFO)
showed that LC50's of Mal-Resistant strains had higher EST. activiy (4.71) with lower MFO activity (3.80),while
,LC50's of Vert-Rresistant strains had lower EST. activiy (2.70) with higher MFO activity (4.26). Synergist experiments
showed low synergism by S,S,S tributylphosphorotrithioate (DEF) of EST activiy ranged from 4.81 to 2.99 folds,while
synergism by Piperonyl Butoxide (PBO) of MFO activity ranged from 4.27 to 3.82folds to LC50's pesticides resistant
strains.