Experiments were carried out in the laboratory to determine antifeedant activity of four plant essential oils of Rabdosia rugosa (Wall. ex Benth), Zanthoxylum armatum (DC.), Artemisia maritima (L.) and Colebrookea oppositifolia (Sm.) against four stored product insect pests viz. Tribolium castaneum (Herbst.), Sitophilus oryzae (L.), Stegobium paniceum (L.) and Plodia interpunctella (Hubner). Feeding deterrence indices (FDI) showed that the plant essential oils had antifeedant action against the four insect pests at different concentrations. R. rugosa and Z. armatum oil at a high concentration of 300 µl/g resulted in 5.22 ± 0.21 and 6.42 ± 0.32% grain damage as compared to 70.32 ± 0.28% damage under control and FDI of 86.17 ± 0.25 and 85.71 ± 0.27% was recorded for T. castaneum followed by S. oryzae with a FDI of 70.58 ± 0.21 and 67.68 ± 0.19% and grain damage of 15.42 ± 0.12 and 16.31 ± 0.21% as compared to 85.36 ± 0.09% grain damage in control for similar concentrations of above oils. A. maritima oil at 100 µl/g showed 76.31 ± 0.16% FDI followed by C. oppositifolia oil obtaining 75.11 ± 0.35% feeding deterrence against T. castaneum whereas 65.99 ± 0.32% and 65.46 ± 0.14% FDI was obtained for similar concentrations of these oils against S. oryzae. FDI of 62.82 ± 0.32 and 60.03 ± 0.26% was observed for R. rugosa and Z. armatum oil at 300 µl/g against S. paniceum followed by 64.97 ± 0.14 and 53.35 ± 0.18% against P. interpunctella for similar concentration of oils. The present study indicated that R. rugosa and Z. armatum were highly effective followed by A. maritima and C. oppositifolia against all the insect pest.

Fumigant toxicity of eight essential oils obtained by hydrodistillation from eight plant species viz. Artemisia maritima L., Cinnamomum zeylanicum Blume, Citrus hystrix DC., Colebrookea oppositifolia Sm., Pelargonium hortorum Bailey, Rabdosia rugosa Wall. ex Benth, Thuja occidentalis L. and Zanthoxylum armatum DC. were tested against different immature stages of Tribolium castaneum (Herbst) and Plodia interpunctella (Hubner) both are serious pests of stored products worldwide. 8-10 day and 18-20 day old larvae of P. interpunctella and T. castaneum were used for the bioassay. R. rugosa oil gave 80.03±5.6% mortality at 100 µl/ml followed by 72.28±4.9% at 50 µl/ml against 8-10 day old larvae. Whereas 65.47±2.9% mortality at 100 µl/ml followed by 62.09±1.8% mortality at a dose of 50 µl/ml was obtained against 18-20 day old larvae of T. castaneum after 120 hrs. At a lowest concentration of 10 µl/ml R. rugosa oil produced 53.8.33±2.2 % mortality for 8-10 day old larvae and a mortality of 40.55±3.9% respectively was obtained for 18-20 day old larvae of P. interpunctella after 120 hrs. Among eight essential oils tested R. rugosa had the highest toxicity followed by A. maritima, C. zeylanicum, Z. armatum, T. occidentalis, P. hortorum, C. oppositifolia and C. hystrix against both the insect pests. The results obtained also showed that tolerance increases as the immature stages grow older and 18-20 day old larvae were least susceptible to all the treatments as compared to 8-10 days old larvae. Larvae of T. castaneum were found to be most susceptible for all treatments than P. interpunctella.