Effect of mycophagous insect on the incidence of sugar beet damping-off caused by R. solani was studied. In the artificially-infested soils, the addition of larvae of Pnyxia scabiei reduced the incidence of the damping-off in comparison with the non-added control. However, the disease was not suppressed by dead larvae killed by isoxathion (insecticide) or propylene oxide. Subsequent tests with non-sterilized soil, naturally infested with Pythium spp. or supplemented with sclerotia of R. solani, revealed that added larvae in a paper-pot provided significant protection of seedling disease.