Effect of some botanical oils on the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae)

Six botanical oils of clove, Tugenia aromatica, anise, Pimpinella anisum, chamomile, Matricaria recutita, cumin, Cuminum cyminum, basil, Ocimum basilicum and lupine, Lupinus albus were tested to determine their insecticidal properties against Sitophilus granarius on wheat grains. Considering the percentage of mortality, the toxicity of oils increased gradually with increasing concentrations. Anise oil had the lowest LC50 followed by clove ˂ basil ˂ chamomile ˂ cumin ˂ lupine. Mortality rates of adult weevils was high at the initial time up to 6 weeks post exposure to grains pre-treated with the tested botanical oils at LC50 Level. Thereafter, the activity gradually decreased over time. Both LC50 and LC99 of anise oil prevented weevilsÂ’ oviposition on treated wheat grains. At both LC50 and LC99 values, no adults emerged from eggs laid on grains pretreated with clove and chamomile. At LC50, very few adults emerged from eggs laid on grains pretreated with cumin, lupine and basil in comparison with the control. In addition, the effects of these oils on water absorption and seed germination of treated wheat grains stored for up to 18 weeks was studied. In general, either LC50 or LC99 values of tested oils showed negligible reduction in water swelling capacity (WSC) of treated wheat seeds at the initial time or even after long time of storage. The results also showed negligible decrease in germination of wheat grains treated with tested oils at LC50 and LC99 levels even 18 weeks post-treatment. This study suggests that the use of these botanical oils, especially anise oil, may be effective to protect wheat seeds from stored grain pests in storage.