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Abstract
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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 μg/larvae, respectively. The insecticidal activity was increased by binary
mixtures of thymol + γ-terpinene or p-cymene, while the composition of p-cymene + γ-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
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