Thiamethoxam insecticide molecule. Computer artwork showing the structure of a molecule of the insecticide thiamethoxam. Thiamethoxam is a broad-spectrum neonicotinoid insecticide that is effective against a wide variety of insects. It is absorbed quickly and transported to all parts of the plant, where it acts as a deterrent to insect feeding. Atoms are coloured coded: carbon (light blue), hydrogen (light green), oxygen (red), sulphur (yellow), chlorine (dark green), nitrogen (dark blue); with the bonds between them shown as rods.