Re-evaluation of recommended insecticides for resistance development, cross-resistance pattern, and underlying mechanisms in Helicoverpa armigera (Lepidoptera: Noctuidae).

The rise of insecticide resistance threatens biodiversity and agricultural sustainability as insects develop mechanisms like enhanced detoxification to withstand toxic exposures. This study assessed resistance levels of Helicoverpa armigera (Lepidoptera: Noctuidae) populations from various regions of India to emamectin benzoate, indoxacarb, spinetoram, and lambda-cyhalothrin, and investigated the role of detoxification enzymes in resistance. Field populations showed variable susceptibility, with negligible resistance to emamectin benzoate, indoxacarb, and spinetoram. Among the tested H. armigera populations, the MaY strain exhibited the highest resistance levels, especially to lambda-cyhalothrin (RR = 45.05), while the KaB and AnN strains showed moderate resistance, and the UtJ, MaS, and RaJ strains remained largely susceptible. Cross-resistance analysis revealed strong resistance in the MaY strain to pyrethroids (RR = 41.06-48.06) but negligible cross-resistance to diamides and broflanilide (RR ≈ 1), with heatmap correlations confirming class-specific resistance patterns. Synergist bioassays showed that piperonyl butoxide (PBO) and triphenyl phosphate (TPP) significantly increased lambda-cyhalothrin toxicity in the MaY strain (up to 9.44-fold), highlighting the involvement of cytochrome P450 monooxygenases (CYP-450) and carboxylesterases (CarE) in metabolic resistance. Detoxification enzyme activity varied significantly between body tissues, with the fat-body showing the highest CYP-450 and CarE levels in the resistant MaY strain. Synergist treatment markedly reduced these activities (Synergistic ratio up to 6.85), especially in fat-bodies, indicating their major role in metabolic resistance. These findings emphasize the urgent need for region-specific resistance monitoring and the integration of synergists and insecticides with novel modes of action to sustain effective control of H. armigera and delay resistance development.