Toxicity of the Lippia gracilis essential oil chemotype, pinene-cineole-limonene, on Spodoptera frugiperda (Lepidoptera: Noctuidae).
Lippia gracilis Schauer, Verbenaceae, is a plant popularly known as "Alecrim-da-Chapada" or "Alecrim-de-Serrote", characteristic of the savanna areas in North and Northeast Brazil. Its essential oil has been tested for pest control due to its bioactive potential. In this work, the chemical composition was analyzed and the insecticidal effect of the pinene/cineol/limonene chemotype leaf oil of L. gracilis, from Chapada das Mesas, Maranhão State, was tested against the armyworms Spodoptera frugiperda (Lepidoptera: Noctuidae). GC and GC-MS analysis identified α-pinene (24.5%), 1,8-cineole (16.2%), β-pinene (11.9%) and limonene (9.6%) as the main constituents of the oil, which presented a yield of 4.3%. For the insecticidal activity, the topical and surface contact tests were carried out with ten-days armyworm's larvae (third instar), in different concentrations of oil and α-pinene, its main constituent. For the oil, the acute topical toxicity (LD50) was 0.09 μL/insect, and the contact surface toxicity (LC50) was 1.55 μL/cm2, while for α-pinene these values were (LD50) 0.28 μL/insect and (LC50) 2.50 μL/cm2, respectively. Thus, the oil was more active than α-pinene showing that the insecticide effect is due to the synergistic action of the mixture of its constituents. The results lead to the conclusion that the essential oil is promising as a sustainable tool in the management of S. frugiperda.