Diatomaceous earth used against insect pests, applied alone or in combination with Metarhizium anisopliae and Beauveria bassiana

Laboratory bioassays were conducted to assess the insecticidal efficacy of the formulation SilicoSec® used alone or in combination with isolates of entomopathogenic fungi, Metarhizium anisopliae (Metschinkoff) Sorokin and Beauveria bassiana (Balsamo) Vuillemin. SilicoSec® is a commercial diatomaceous earth (DE) formulation. Wheat was treated with 200 mg/kg of DE, 400 mg/kg of each isolates alone or a combination of them, against Tribolium castaneum Herbst, Rhyzopertha dominica (F.), and Oryzaephilus surinamensis L. The experiments were carried out at 27±1°C and 65±5% relative humidity (RH) in continuous darkness. The pathogenicity of all isolates was significantly low even after 7 days of exposure, with the exception of R. dominica. The isolates were virulent to the beetles, but the efficacy of the isolates was enhanced in combination with the DE. Tribolium castaneum was the most resistant species, followed by R. dominica. The findings indicated that the addition of the DE to the isolates increased the pathogenicity especially at the highest exposure interval. The addition of DE may provide satisfactory control of the insect-pests of stored products.