Biochemical Mechanism of Insecticide Resistance in Plutella xylostella (L.) Collected from Three Locations of Varanasi, U.P.

To determine the activity of carboxylesterase (CE) involved in degradation of toxic chemicals, a specific CE hydrolysahle chemical alpha naphthyl acetate (α-na) was used as a substrate. The activity of CE ranged from 7.27–16.60, 7.19–17.03 and 5.85–14.32 m moles α-na hydrolysed per mg protein per min on cabbage and 6.08–21.06, 4.63–19.13 and 3.14–15.61 m moles α-na hydrolysed per mg protein per min on cauliflower in Karsara, Madaon and Tikari, respectively, during 1998. In 1999, the CE activity ranged from 9.25–16.15, 7.70–16.76 and 6.19–17.08 m moles α-na hydrolysed per mg protein per min on cabbage and 7.08–20.46, 5.82–19.66 and 4.83–17.56 m moles α-na hydrolysed per mg protein per min on cauliflower in all the three villages, respectively. The enzymic activity was lower in Tikari as compared to Karsara and Madaon. The use of synergist PBO (MFO inhibitor) resulted in MFO inhibition significantly during all the months under study. The MFO inhibition in Madaon ranged from 16.20–27.85 and 21.0–35.06% during the entire season in 1998 and 1999, respectively. The corresponding figures in Tikari varied from 15.35–25.16 and 16.0–27.75% during 1998 and 1999, respectively. These findings when compared to respective resistance level indicated higher resistance met with higher CE activity.