Abstract Range‐finding studies on the toxicity of cyanogen to all stages of five species of stored product Coleoptera are reported. The species were Rhyzopertha dominica (F), Sitophilus granarius (L), Sitophilus Oryzae (L), Tribolium castaneum (Herbst), Tribolium confusum Jacquelin du Val and Ephestia cautella (Walker). Exposures for 24 h to cyanogen at 1.3 mg litre −1 controlled all external stages. Control of internal stages of Sitophilus species was achieved by a 5‐day exposure to initial concentrations between 13.7 and 27.4 mg litre −1 , whereas R dominica was controlled at 13.7 mg litre −1 . Cyanogen showed similar toxicity to all tested external stages and, in this respect, was more similar to methyl bromide than to phosphine. Its toxicity to insects increased with both relative humidity and concentration of carbon dioxide. Cyanogen was toxic to insects whether applied as a gas or in an aqueous solution. © 2003 Society of Chemical Industry