Essential oils of Piper subtomentosum (leaves and inflorescences) and Piper septuplinervium (aerial parts) were analyzed by GC-MS; sixty-three compounds were determined, representing 92.0%, 86.9 %, and 91.8 % of the total relative oil composition of the leaves, inflorescences, and aerial parts, respectively. The most abundant component in the aerial parts and inflorescence oils was α-pinene (27.3%, 21.0%, respectively), and δ-cadinene was the main component of the leaf oil. Insecticidal activity of the essential oils were determined on the Spodoptera frugiperda second instar larvae; the essential oil from the aerial parts of P. septuplinervium was the most active against insect pests (LC50= 9.4 μL/L of air). Statistical analysis by direct Pearson correlation showed that the insecticidal activity of the essential oils was primarily due to camphene and α- and β-pinene. The effect of the oils on the insect life cycle was also evaluated, and in some cases, a delay in growth and inhibition of the oviposition in the females were observed.