Insecticidal Potential of Essential Oil and Sesquiterpene Alcohols from Leaves of Clausena indica (Dalz.) Oliver Against Spodoptera litura, Helicoverpa armigera, and Tribolium castaneum Under Laboratory and Field Conditions.

Insects, due to their unrestricted reproduction, have been a long-known nuisance causing significant damage to various crops. Besides the synthetic chemical pesticides, the bioactive compounds derived from medicinal plants also make a positive contribution against the control of pests. In this concern, the present study investigated the biological activity of essential oil and isolated sesquiterpene alcohols, τ-cadinol and β-bisabolol, from Clausena indica leaves against three insect pests, Spodoptera litura, Helicoverpa armigera, and Tribolium castaneum. Four different concentrations (25, 50, 75, and 100 g L) of oil, τ-cadinol, and β-bisabolol in both normal and microencapsulated forms were tested for their efficacy in the field trial. Among all the compounds, τ-cadinol exhibited strong toxicity (LD = 35.93-52.94 µg larva), antifeedant activity (DC = 52.51-75.93 µg cm), and oviposition deterrent activity (OD = 56.73-67.18 µg cm) against all the tested pests followed by β-bisabolol and leaf essential oil. Additionally, both the compounds demonstrated noteworthy acetylcholinesterase inhibitory activity with IC values of 24.53-30.98 μg mL and 32.15-40.41 μg mL respectively comparable to the positive control, galantamine. Moreover, both τ-cadinol and β-bisabolol exhibited the strongest cytotoxicity against Sf9 cells lines with IC of 15.27 and 17.82 µg mL respectively while IC of 5.02 µg mL was shown by azadirachtin on the same cell line. Results of the field trial reveal that all tested compounds showed considerable mortality of S. litura and H. armigera. Although the treatments showed good insecticidal activity in the field trial, but modifications are required for the concentration of active ingredients in the formulation or even in the formulation to enhance the effect. The results obtained lay a foundation for future field applications of oil and isolated compounds as crop protectants.