Toxicity of some Plant Oils under Different Temperatures against Stored Grain Insects, Sitophilus oryzae and Rhyzopertha dominica

Sitophilus oryzae and Rhyzopertha dominica are serious insect pests of stored products in Egypt. The use of plant materials rather than conventional insecticides to control these insects is a promising alternative to neurotoxic insecticides. In this study, the efficiency of four plant oils, wormwood (Artemisia absinthium), marjoram(Origanum majorana), jojoba (Simmondsia chinensis)and argan (Argania spinose) against these pests were evaluated at three degrees of temperature, 25, 30 and 35 ˚C. Further, the persistence and long-active effectiveness of the testing essential oils after a specific period of storage were evaluated. Results showed that wormwood oil exhibited the highest efficiency on R. dominica at 30 ºC with LC50 values of 3.27 μg /ml, while argan oil exhibited the highest effect at 35 ºC with LC50 values of 3.48 μg /ml after three days post treatment. Jojoba oil showed the highest efficiency on S. oryzae followed by argan, wormwoodand marjoramat 30º and 35 ºC after 72 h. After six months of storage, all tested oils lost their efficiency against S. oryzae and R. dominica at 25º and 35 ºC.