(Cabrera) H. Rob. (Asteraceae), an endemic species from the north of Argentina, is a rich source of elephantopus-type sesquiterpene lactones. These compounds have proved to be promising antiparasitic agents, but there is no report about their action against pest insects. In this work we studied for the first time the antifeedant and toxic effects of natural products against the fall army warm Smith and the oviposition deterrent activity against the fruit fly Wiedemann. As a result, we found that extracts, fractions composed of sesquiterpene lactones and pure sesquiterpene lactones altered larval feeding behavior in the food choice test. Nutritional parameters of . larvae were also affected. Fraction II (300 μg/g of diet.), containing compounds , and , was the most toxic substance with 80% pupal mortality and wing malformations in adults. In oviposition deterrent experiments against , we observed a moderate effect at 30 μg/cm of the test compound. The most active substances were the methanolic extract, dichloromethane subextract and lactone . According to our results, natural products could be used for maximizing the effectiveness and specificity in future insecticide design with specific or multiple target sites, while ensuring the economic and ecological sustainability, in addition to combat the increasing resistance rates developed by synthetic pesticides.