LAUSR

Abstract Spodoptera litura (Fabricius) is an important polyphagous insect pest of several host plants worldwide and has developed resistance to many insecticides. The present study aimed at analysing the effect of selection with fenvalerate on a resistant field population from Sangrur, Punjab, India (SGR) through synergist and biochemical assays. Following selection with fenvalerate for 14 generations, the selected population (SGR-Sel) was analysed through bioassays to assess changes in levels of resistance, synergism and detoxification enzyme activities. Resistance ratio increased from 12.61 to 52.81 fold when compared to the laboratory susceptible strain (H-Sus). Synergism of piperonyl butoxide (6.19 fold) and triphenyl phosphate (5.88) was observed with SGR-Sel, which suggested the involvement of mainly monooxygenases (mixed function oxidases or MFOs) and esterases in resistance to fenvalerate. A strong positive correlation (r = 0.98) was observed between MFO activity and fenvalerate resistance in SGR-Sel, the activity was 4.26- and 1.84- fold that of H-Sus and SGR. Similarly, esterase activity was 3.70- and 1.73- fold that of H-Sus and SGR populations, with a strong positive correlation between esterases and fenvalerate resistance (r = 0.97). Alignment between COI sequences of SGR-Sel and SGR identified the existence of a single base/nucleotide polymorphism at position 421 represented by replacement of C in SGR with T in SGR-Sel. In the translated protein sequence, serine in SGR was replaced by phenylalanine in SGR-Sel population at position 139.