Insecticidal efficacy of spinosad, Beauveria bassiana and Metarhizium anisopliae in combination with diatomaceous earth, for controlling Sitophilus oryza (L.) (Coleoptera: Curculionidae) infesting stored wheat

Laboratory experiments were carried out in order to evaluate the insecticidal effect of three bio-insecticides (i.e., Spinosad, Beauveria bassiana and Metarhizium anisopliae) against Sitophilus oryzae on wheat. In parallel, wheat was treated with diatomaceous earth (DE) at one dosage rate, 2 g/kg of wheat either alone or in combination with three bio-insecticides applied at three dosage rates for each. Mortality of adults was counted 24 h, 48 h, 7 days, and 14 days later. In general, the combination of DE with three bio-insecticides increased the mortality rates of S. oryzae compared with treatments alone due to a potential additive effect. The highest spinosad/DE dosage combination resulted in the greatest mortality against S. oryzae compared with other treatments at all exposure periods. Moreover, significantly less progeny were produced on wheat treated with the highest dosage of spinosad with DE, in comparison with the other treatments. The results of this study suggest that bio-insecticides can be used effectively with DE against S. oryzae by exhibiting additive effect