Abstract: The present study has been undertaken to find out the effectiveness of DE and some other inert dusts like, kaolin powder, paddy husk ash, coal ash, alluvial soil, china clay and a dust formulation insecticide carbaryl on the cowpea beetles Callosobruchus maculates (F. ). The bioassay of the dusts was done on adult beetles by applying them with normal food. The LD50 of C. maculatus after 24 h was 737.15, 73305.15, 1479.29, 11449.60, 117371.50, 5171.79 and 21.49 ppm for diatomaceous earth, kaolin powder, paddy husk ash, coal ash, alluvial soil, china clay and carbaryl, respectively. The LD50 after 48 h was 385.24, 12078.10, 974.11, 7433.71, 10650.42, 1168.22 and 11.25 ppm for diatomaceous earth, kaolin powder, paddy husk ash, coal ash, alluvial soil, china clay and carbaryl respectively. The order of toxicity of the insecticides was carbaryl > diatomaceous earth > paddy husk ash > china clay > coal ash > alluvial soil> kaolin powder.