【Aim】 To clarify the relatively sensitive baselines and resistance levels of Spodoptera frugiperda to five commonly used insecticides in Fujian Province, and evaluate the sensitivity of young larvae of S. frugiperda to these insecticides. 【Method】 The toxicities of the five commonly used insecticides towards the 1st and 2nd instar larvae of the relatively sensitive population of S. frugiperda were determined using the leaf dipping method. Monitoring resistance of S. frugiperda populations from three different regions to these insecticides was performed. The 95% confidence limits of LC₅₀ values that did not overlap were used as the criterion for judging the significant differences in sensitivity of the same instar larvae from different geographical populations or between the 1st and 2nd instar larvae of the same population to the same insecticide. 【Result】 The toxicities of the five insecticides to the larvae of the relatively sensitive population of S. frugiperda were as follows: emamectin benzoate>spinetoram>chlorantraniliprole>lufenuron>indoxacarb. The insecticides exhibited higher toxicity to the 1st instar larvae than to the 2nd instar. The data obtained in the toxicity testing of emamectin benzoate, spinetoram, and lufenuron on the 1st instar larvae of S. frugiperda showed a smaller chi-square value and larger P-value than that for the 2nd instar larvae, whereas in the toxicity testing of chlorantraniliprole and indoxacarb, the 1st instar larvae showed slightly larger chi-square value than that for the 2nd instar larvae, but their P-values were both above 0.9190. The results indicated that the degree of resistance of S. frugiperda field populations from the three different regions to emamectin and indoxacarb was at the stage of decreased sensitivity to low-level resistance in Fujian, and that the pest had developed low resistance to chlorantraniliprole. The degree of resistance of the three different geographical populations to spinetoram was at the stage of decreased sensitivity, however all populations maintained sensitivity to lufenuron. 【Conclusion】 The population of S. frugiperda remained sensitive to lufenuron in Fujian Province. Overall, the resistance degree of the pest was at a stage of decreased sensitivity or low-level resistance to the other four common insecticides. Both the 1st and 2nd instar larvae are suitable for the toxicity testing of insecticides against S. frugiperda; however, the 1st instar larvae that hatched within 12 h without feeding are more suitable than the 2nd instar larvae.