Insecticidal potential of Ajwain essential oil and its major components against Chilo suppressalis Walker

Essential oils and their constituents are presently known to interfere with herbivorous insects' behavioral and physiological activities. The effects of Ajwain (Carum copticum, L.) (Apiaceae) essential oil (AEO) and its main components were studied on Chilo suppressalis Walker (Lepidoptera: Crambidae), a serious pest of rice cropping in several parts of the world. The study included the toxicity of each component of AEO and the estimation of their synergistic or antagonistic effect on C. suppressalis larvae. The bioassay data showed the high insecticidal activity of AEO and thymol against the C. suppressalis larvae with LD50 values of 13.10 and 17.11 mu g/larvae, respectively. The insecticidal activity was increased by binary mixtures of thymol + gamma-terpinene or p-cymene, while the composition of p-cymene + gamma-terpinene showed an antagonistic effect on the insects. The biochemical experiments demonstrated that treatment of AEO and its components enhanced the activities of detoxifying and antioxidant enzymes, and inhibited acetylcholinesterase. Among these compounds, thymol may be recommended as a potent biopesticide in controlling C. suppressalis populations, both insecticidal and compatible with other components with high AChE inhibition properties.