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Background: The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), was recorded for the first time in Pakistan in 2019, and now it has spread in several regions, i.e., Punjab and Sindh, affecting maize production. Farmers are using widely synthetic pesticides to control the pest. Further, the resistance development in insects and the non-target effect of chemicals on the environment and humans pose serious threats of using insecticides. The use of entomopathogenic fungi (EPF) is being considered an important tool in integrated pest management program. The main objective of this study was to check the impact of different conidial concentrations of Metarhizium anisopliae fungus on the nutritional physiology of S. frugiperda. Results: The dose-dependent effect of tested EPF was observed, and the highest concentration (1 × 109 conidia/ml) considerably affected nutritional parameters. Reduced relative consumption rate (21.7%), relative growth rate (19.5%), the efficiency of conversion of ingested food (24.2%), and approximate digestibility (16.3%) were observed in treated larvae compared to the untreated by using a higher concentration of EPF. Pupal weight was also found lower (77.9 mg and 84.2 mg, respectively), when larvae were treated by 1 × 109 and 1 × 108 conidia/ml concentrations of EPF. Further, 46.7% of larvae were found dead with this conidial concentration. Conclusions: This study suggests that the application of a higher concentration of M. anisopliae could be an effective option to control S. frugiperda. The EPF can enhance the integrated pest management programs and could be useful in reducing the environmental impact of synthetic insecticides. [ABSTRACT FROM AUTHOR]