A particulate composition comprises from 40 to 80% by weight of a water-soluble saccharide, from 1.5 to 10% by weight of a finely particulate amorphous hydrophobic silica having a surface area in the range of from 80 to 300 m.sup.2/g and water. The composition is in the form of fine particles of an aqueous solution of the water-soluble saccharide, the surfaces of which fine particles of aqueous solution are coated with a coating of the finely particulate amorphous hydrophic silica.The composition, which may additionally contain one or more biocidally-active materials, can be applied through conventional dust applicator equipment for the treatment of pests.