The objective of this study is to investigate the bioactivity of ethanolic extract derived from Asclepias curassavica L. on Spodoptera frugiperda (Lepidoptera: Noctuidae). In two bioassays, different concentrations of the plant extract (bioassay 1: 1%, 2%, and 4%; bioassay 2: 0.05%, 0.1%, and 0.5%) were administered to the caterpillars through the diet. All the tested concentrations of A. curassavica extract, added to an artificial diet, induced the death of S. frugiperda. Prolonged larval periods were detected in S. frugiperda treated with the 0.1% and 0.5% extracts. Moreover, 0.05%, 0.5%, 1%, 2%, and 4% extracts induced a reduction in the larval weight. The weight of male pupae was significantly lower in the 0.05, 0.1, and 0.5% treatment groups than in the control group. Moreover, 0.1% extract induced a reduction in the weight of female pupae by 9.5%. Food intake was reduced by the treatment with 0.05%, 1%, 2%, and 4% extracts. The extracts, at different concentrations, did not affect the number of lays, number of eggs, and hatching percentage. The outcomes indicate that the ethanolic extract of A. curassavica, acquired at the reproductive phase of this plant, is effective in controlling the population of S. frugiperda.