Field populations of Diamondback moth, Plutella xylostella (L.), were selected with four insecticides, indoxacarb, cypermethrin, Neemazal-F^TM and aqueous extract of neem seeds, neem seed kernel extract - NSKE. The activity of MFOs (para-nitroanisole), esterases (α , β-NA) and glutathione-S-transferases (CDNB & DCNB) were assayed in the selected and unselected strains. The activity of the MFOs was highest in JCyp-R (4.26 ± 0.77 ηmole/mg protein/min) strain resistant to cypermethrin, followed by JInd-R (indoxacarb resistant) (3.65 ± 0.44 ηmole/mg protein/min) strain, and was more in all selected strains compared to unselected strains. Activity of the esterases was highest in JInd-R (0.82 ± 0.14 µmole of α-naphthol /mg of protein/min). Activity levels of esterases recorded in JNzF-R (Neemazal-FTM resistant strain) and JNSKE-R (NSKE resistant) strains were below that of the unselected strains. Higher activity of GSTs in JInd-R strain was evident when both DCNB (56.18 ± 16.12 µmole /mg of protein/min) and CDNB (66.38 ± 10.68 µmole/mg of protein/min) were used as substrates. The activity levels of NSKE and Neemazal-F^TM selected strains were however, quite low against these substrates. Thus the indoxacarb resistance in DBM may be due to any and all of the three groups of detoxifying enzymes while that of cypermethrin was largely governed by MFOs. Unlike synthetic insecticides, NSKE and Neemazal-F^TM selected populations indicated loss of proteins suggesting reduced overall enzyme activity. Loss of proteins in neem selected P. xylostella strains may indirectly suggest the possibility of Built in Resistance Prevention Mechanism associated with neem.