Insecticidal activity of Piper essential oils from the Amazon against the fire ant Solenopsis saevissima (Smith) (Hymenoptera: Formicidae)

Pepper plants in the genus Piper (Piperales: Piperaceae) are common in the Brazilian Amazon and many produce compounds with biological activity against insect pests. We evaluated the insecticidal effect of essential oils from Piper aduncum, Piper marginatum (chemotypes A and B), Piper divaricatum and Piper callosum against workers of the fire ant Solenopsis saevissima (Smith) (Hymenoptera: Formicidae), as well as their chemical composition by gas chromatography and gas chromatography–mass spectrometry. The lowest median lethal concentration (LC50) in 48 h was obtained with the oil of P. aduncum (58.4 mg/L), followed by the oils of P. marginatum types A (122.4 mg/L) and B (167.0 mg/L), P. divaricatum (301.7 mg/L), and P. callosum (312.6 mg/L). The major chemical constituents were dillapiole (64.4%) in the oil of P. aduncum; p-mentha-1(7),8-diene (39.0%), 3,4-methylenedioxypropiophenone (19.0%), and (E)-β-ocimene (9.8%) in P. marginatum chemotype A and (E)-isoosmorhizole (32.2%), (E)-anethole (26.4%), isoosmorhizole (11.2%), and (Z)-anethole (6.0%) in P. marginatum chemotype B; methyleugenol (69.2%) and eugenol (16.2%) in P. divaricatum; and safrole (69.2%), methyleugenol (8.6%), and β-pinene (6.2%) in P. callosum. These chemical constituents have been previously known to possess insecticidal properties.