The fall armyworm Spodoptera frugiperda (JE Smith) is a polyphagous insect that causes losses to farmers in the world. This work was aimed isolating and identifying the active substances produced by Duguetia lanceolata A. St. Hil for S. frugiperda. The dichloromethane soluble fraction from D. lanceolata stem bark, incorporated into an artificial diet for S. frugiperda, showed high insecticidal activity against this insect (LC50 = 295 μg mL−1 of diet). Its fractionation yielded two aporphine alkaloids and a mixture of trans-asarone and 2,4,5-trimethoxystyrene, which was active against S. frugiperda (LC50 = 124 μg mL−1 of diet). Both trans-asarone and 2,4,5-trimethoxystyrene were individually active against the insect, with the latter substance being more active (LT50 = 73 h) than the former (LT50 = 170 h). In conclusion, trans-asarone and 2,4,5-trimethoxystyrene are the substances produced by D. lanceolata that are active against S. frugiperda. © 2019 Elsevier Ltd