Detoxification enzyme inhibitor mediated synergism of insecticide toxicity in Spodoptera frugiperda (Lepidoptera: Noctuidae)
Insecticide efficacy against the maize fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is closely linked to metabolic detoxification processes that can be influenced by the use of synergists. This study assessed the effect of five selected synergists on the toxicity of five commonly used insecticides against third-instar larvae collected from 2 locations in Odisha, namely Bhubaneswar and Bhawanipatna, under laboratory conditions. In the Bhubaneswar population (BBPL), lambda-cyhalothrin exhibited the highest synergism with piperonyl butoxide (PBO) and N-(propargyloxy) phthalimide with synergistic ratios (SR) of 6.50 and 4.41 respectively. Acephate recorded the highest synergism with triphenyl phosphate (TPP) (SR = 5.85). Diethyl maleate (DEM) showed greater synergism with emamectin benzoate (SR = 3.91) and spinetoram responded notably to PBO (SR = 4.20). In contrast, the Bhawanipatna population (BPPL) showed a stronger and more consistent response to DEM with all five insecticides, with SR values of 6.71 for lambda-cyhalothrin, 6.20 for acephate, 5.10 for spinetoram and 4.76 for emamectin benzoate. Chlorantraniliprole exhibited comparatively lower synergistic responses with most synergists, although DEM produced a substantially higher synergistic ratio in BPPL (SR = 4.39). The least effective synergist was 5-nitrouracil (1.25–1.72) in both populations, indicating a minimal role of uridine diphosphate glycosyltransferases (UGTs) mediated detoxification pathways. The difference in synergistic response between populations suggests involvement of different detoxification enzymes in both populations. Cytochrome P450 monooxygenases and carboxyl esterases appear more influential in BBPL while glutathione S-transferases (GST) are more significant in BPPL. These findings highlight the potential of synergists to improve insecticide efficacy and strengthen insecticide resistance management (IRM) strategies.