Chemical composition, and insecticidal activities of four plant essential oils from Morocco against larvae of Helicoverpa armigera (Hub.) under field and laboratory conditions
Aromatic and medicinal plants are a rich source of molecules with insecticidal activities against many insect pests. The present study investigated the insecticidal activities of four essential oils against the third instar larvae of Helicoverpa armigera. Contact toxicity and systemic toxicity of essential oils were assessed toward third instar larvae of H. armigera using three concentrations under laboratory conditions. While under field conditions, the experiment was conducted in a randomized complete block in three replications using the most effective oils. The Ocimum basilicum essential oil showed a high level of larvicidal activity at 2.5% with 88% and 92% of larval mortality after 24 h and 48 h of application, respectively. Mentha spicata oil caused 2.5%, 52% and 76% larval mortality after 24 h and 48 h of application, respectively. As for the topical application, O. basilicum at 2.5% and 5% concentrations, caused 80% and 100% larval mortality after 24 h of treatment, respectively. M. spicata at 5% induced 80% and 100% larval mortality after 6 h and 24 h of application, respectively. The field data confirmed the significant effect of O. basilicum oil at 2.5% in reducing the pod borer larvae and pod damage after 6 days of the first and second spray, compared to the control. GC-MS revealed that the major compounds of O. basilicum essential oil were Estragole (78.94%) and Linalool (16.61%), whereas M. spicata essential oil had Cis-carvyl acetate (63.69%) and D-limonene (14.79%) as major components. These results suggest the potential use of O. basilicum and M. spicata essential oils for the development of ecofriendly, safe and effective biological insecticides for the control of chickpea pod borer.