Turmeric, Curcuma longa L. (Zingiberaceae) has well-known insecticidal and repellent effects on insect pests, but its impact on the Maize weevil Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae) and the fall armyworm Spodoptera frugiperda J.E. Smith, 1797 (Lepidoptera: Noctuidae) is unknown. In this study, we evaluated the insecticidal and repellent effects of ar-turmerone, extracted from rhizomes of C. longa, on the S. zeamais and S. frugiperda. Individuals of S. zeamais died after six days of contact with ar-turmerone at 1% (mm⁻¹), while individuals of S. frugiperda showed a 58% mortality rate after ingestion of this compound at 1% (mv⁻¹). The width of head capsule, and length and weight of body of surviving S. frugiperda caterpillars exposed to ar-turmerone were 60.0, 59.6 and 93.8% lower than those of control caterpillars, respectively. Dry weight of ingested food, feces produced, weight gain and dry weight of food assimilated and metabolized by surviving S. frugiperda caterpillars were lower with artificial diet with ar-turmerone. Hatching of caterpillars from newly laid, 1- or 2-day-old S. frugiperda eggs was 48.6, 14.2 and 48.5%, respectively. Ar-turmerone is highly toxic to S. zeamais and S. frugiperda at low doses.