Evaluation of Insecticide Resistance and Associated Enzyme Activity in Field Populations of Diamondback Moth ( <scp> <i>Plutella xylostella</i> </scp> )

The diamondback moth, Plutella xylostella (L.), is a major pest of cruciferous crops with a remarkable capacity to develop insecticide resistance. The present study evaluated the susceptibility, resistance ratios, and detoxification mechanisms of field populations collected from Andhra Pradesh, India, against tolfenpyrad 15 EC and emamectin benzoate 5 SG. Laboratory selection studies revealed declining LC₅₀ values over successive generations reared without insecticide pressure, indicating partial recovery of susceptibility. Field bioassays showed resistance ratios ranging from 9.8 to 13.1 for tolfenpyrad and 5.3 to 10.2 for emamectin benzoate, with the Ponnur population exhibiting the highest resistance levels. Biochemical assays demonstrated that tolfenpyrad resistance was primarily associated with increased glutathione-S-transferase (GST) activity, while emamectin benzoate resistance was largely mediated by elevated carboxylesterase (CarE) activity, supported by moderate induction of mixed-function oxidases (MFOs). Specifically, GST activity increased by 2.06-fold and CarE activity by 1.90-fold in resistant populations compared with the susceptible strain, confirming the role of detoxification enzymes in resistance development. These findings highlight distinct enzymatic pathways involved in insecticide resistance and emphasize the importance of regular resistance monitoring. Adoption of insecticide rotation with different modes of action, combined with non-chemical pest management strategies, is recommended to prolong the efficacy of these insecticides in crucifer pest management programs.