INSECTICIDES, chemicals used for destroying insect pests. When employed to protect plants they may be applied in the form of wet sprays or as dusts ; those most commonly used for this purpose include various arsenicals, nicotine, oil emulsions, soaps, caustic alkalis, etc. When it is desired to kill insects that may be present in a room, fumigation (q.v.) or the filling of the room with poisonous gases or vapours is resorted to. This method may also be used for plants by enclosing them in tents. Hydrogen cy anide, carbon disulphide and carbon tetrachloride are some ex amples of the chemicals employed in fumigation. (See ENTOMOL OGY, ECONOMIC : Control Measures; Physicochemical Methods.)