Insecticidal activities of Salvia hispanica L. essential oil and combinations of their main compounds against the beet armyworm Spodoptera exigua

Plant essential oils are the powerful candidates to develop natural insect management agents. Their chemical compounds along with their biological activity are often affected by many factors. However, the relationships between the composition and bioactivity of the compounds are not well understood. In this study, eight plant essential oils were screened, and the main compounds from the most effective oil showing insecticidal properties against third-instar larvae of the beet armyworm (Spodoptera exigua Hubner) were evaluated for comparative and synergistic interactions by topical application. The results indicated that Salvia hispanica L. essential oil showed significant insecticidal activity against S. exigua compared with the other seven essential oils. Fifteen major compounds were identified from S. hispanica via gas chromatography-mass spectrometry, with the most abundant compound (α-thujone) possessing the highest insecticidal activity. Several combinations of the four major compounds (α-thujone, (+)-camphor, 1,8-cineole, and α-caryophyllene) from S. hispanica exhibited synergistic insecticidal activities. This study demonstrates the potential of S. hispanica essential oil and α-thujone as effective botanical insecticides in the control of beet armyworm and provides a better understanding of essential oil compound-pest interactions.