High toxicity of camphene and γ-elemene from Wedelia prostrata essential oil against larvae of Spodoptera litura (Lepidoptera: Noctuidae)

The development of eco-friendly biopesticides in the fight against agricultural pests is an important challenge nowadays. The essential oil of Wedelia prostrata Hemsl. is known for its multipurpose biological activities in Chinese folk medicine. However, limited efforts attempted to understand the potential insecticidal activity of its main individual constituents and related mechanism of action. In this research, we investigated the insecticidal activity of W. prostrata against the crop pest Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae). Toxicity on 4th instar larvae was assessed after 24 h of exposure. The LC50 and LC90 of the W. prostrata essential oil were 167.46 and 322.12 mu g/ml, respectively. GC-MS analyses were carried out to shed light on the oil chemical composition. Main constituents were the monoterpene camphene (9.6%) and the sesquiterpenes gamma-elemene (7.6%), alpha-humulene (6.9%), and (E,E)-alpha-farnesene (7.3%). The pure constituents were evaluated for their insecticidal activity on S. litura 4th instar larvae. The most toxic molecule was camphene (LC50 = 6.28 mu g/ml), followed by gamma-elemene, (LC50 = 10.64 mu g/ml), alpha-humulene (LC50 = 12.89 mu g/ml), and (E,E)-alpha-farnesene (LC50 = 16.77 mu g/ml). Overall, our experiments highlighted the promising potential of camphene and gamma-elemene from W. prostrata essential oil against larvae of S. litura, allowing us to propose these two compounds for the development of newer pesticides in the fight against crop pests. Further studies aimed at evaluating the potential synergy between these two molecules, as well as their stability in field conditions are ongoing.