The present invention relates to aqueous insecticidal preparations in the form of an aqueous dispersion of finely divided polymer particles which comprise at least one insecticidal organic active ingredient with a solubility in water of not more than 5 g/l at 25° C. at 1013 mbar and which have a mean particle size, determined by dynamic light scattering, of not more than 300 nm, where the polymer particles which comprise the at least one insecticidal active ingredient of a cationic surface charge and where the aqueous dispersion of the active-ingredient-comprising polymer particles is obtainable by subjecting a monomer composition of ethylenically unsaturated monomers M, in which the ethylenically unsaturated monomers M comprise the at least one insecticidal active ingredient in dissolved form, to radical aqueous emulsion polymerization. The invention also related to the use of such aqueous insecticide compositions for protecting lignocellulosic materials, in particular timber, against attack by harmful insects.