Oxymatrine-based insecticide: A natural product for the control of stored-product beetle pests in wheat grain

Insecticides of natural origin are a promising alternative to synthetic insecticides. Therefore, the intention of this study was to evaluate the potential of the natural product oxymatrine, as a wheat grain protectant against major stored-product beetle pests. The insecticidal activity of oxymatrine was tested against Rhyzopertha dominica (Fabricius, 1792) (Coleoptera: Bostrichidae), Sitophilus granarius (Linnaeus, 1758) (Coleoptera: Curculionidae), Sitophilus oryzae (Linnaeus, 1763) (Coleoptera: Curculionidae), Tribolium confusum (Jacquelin du Val, 1868) (Coleoptera: Tenebrionidae) and Tribolium castaneum (Herbst, 1797) (Coleoptera: Tenebrionidae) at doses of 0.25, 0.5, 1, 2 and 4 mg a.i./kg (ppm) of wheat grain. Initial mortality was assessed after 2, 7 and 14 days of exposure, and total mortality after 7 days of recovery period. The impact on progeny production/reduction was assessed for all species, while in the case of R. dominica and Sitophilus species related weight loss and frass production were also documented. The results show that species, dose, exposure and the recovery period significantly affect the effectiveness of oxymatrine. All doses of oxymatrine provided complete mortality of R. dominica after 7 days of exposure and 7 days of recovery. The satisfactory control of Sitophilus species and T. castaneum was achieved by 1 mg/kg and T. confusum by 4 mg/kg after 14 days of exposure and 7 days of recovery. Oxymatrine complete suppressed progeny production and prevented damage by R. dominica after all exposure intervals. The lowest number of progeny of Sitophilus and Tribolium species and damage by Sitophilus species was recorded after 14 days of exposure in wheat treated with ≥1 mg/kg of oxymatrine. The obtained results indicate that oxymatrine could be an efficient natural product for the control of stored-product beetles in stored wheat.