Evaluation of Dietary Toxicity of some Essential Oil Allelochemicals for The Management of Chilo Partellus (Swinhoe)

Eight essential oil compounds were used for study of larvicidal and growth inhibitory effects against the maize stem borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae). It is the most prevalent key pests, and is one of the limiting factors in the successful cultivation of the maize crop in India. Two dietary bioassays; on-diet and in-diet, were used. The bioassays showed different tenden- cies and LC 50 values were on the lower side in on-diet tests compared to in-diet assays. Thymol was the most active in both laboratory and greenhouse experiments. In greenhouse conditions, thymol was significantly active at a 10 x LC 50 level of treatment. Overall mor- tality due to thymol was 41.66% in 4 days and larvae failed to bore into the plant and could not feed until 48 h post-treatment. After 72 h there was some degree of feeding and boring in the plants by insects, but still < 45% of that in the controls. The present study suggests that larvicidal and growth inhibitory activity by the essential oil compounds could be beneficial as a possible control of the maize borer. This is especially true about thymol which has potential in field situations. It is effective if a proper delivery system and the appropriate time of sprays is established. A 4 day-interval spray of thymol against C. partellus can control the pest significantly and can be used in any integrated pest management system. On the basis of compound structure, no specific trend was observed.