Individual and Synergistic Effects of the Acetonic Extract of <scp> <i>Jatropha curcas</i> </scp> L. (Euphorbiaceae) Seeds and the Enzymatic Extract of <scp> <i>Serratia marcescens</i> </scp> Strain 81 on <scp> <i>Spodoptera frugiperda</i> </scp> (J.

ABSTRACT This study evaluated the insecticidal potential of an acetonic extract from Jatropha curcas seeds (JcAE) and an enzymatic extract from Serratia marcescens (SmEE). The extracts were applied individually or in combination against Spodoptera frugiperda to assess their effects on larval and pupal mortality, weight, and developmental duration. Bioassays were performed via artificial diet incorporation using control (0 ppm), JcAE (100, 250, 1000 and 2500 ppm), SmEE (40, 80, 150 and 300 ppm), and combined JcAE + SmEE treatments (1000 + 150, 1000 + 300, 2500 + 150 and 2500 + 300 ppm). Larval and pupal mortality, weight reduction, and developmental delays were measured. Mortality data were analysed using Fisher's exact test, while weight and development time were compared via Kruskal–Wallis followed by Dunn's tests, with percentage differences calculated relative to the control. The highest concentrations of JcAE (1000 and 2500 ppm) and SmEE (150 and 300 ppm) caused significant insecticidal activity (77.33%–86.67% cumulative mortality), reduced larval weight (−63.02% to—80.23%) and pupal weight (−8.45% to −22.72%), and delayed development by 4–10 days. Synergistic effects were observed in combined treatments (1000 + 300 and 2500 + 300 ppm), which further increased mortality (90.0%–93.33%), suppressed growth, and extended larval development. Chemical analyses identified seven major fatty acids in JcAE, while SmEE exhibited exo‐ and endo‐chitinase activity. These results demonstrate that JcAE and SmEE, alone or in combination, are viable candidates for the agroecological management of S. frugiperda , as they present a double mechanism of action: toxicity and interruption of development, which may help to achieve sustainable crop production.