Persistent Toxicity of Some Organophosphorus Insecticides Against Storage Insect Pests on Wheat

Laboratory studies on persistent toxicity (PT) of three organophosphatic compounds revealed that malathion was persistent at 8 and 12 ppm, and could protect wheat grain from Rhizopertha dominica (F.) for 10 to 12 weeks following treatment. However, pirimiphos-methyl at 12 ppm provided superior protection against Oryzaephilus surinamensis (L.) and Tribolium confusum (Jacq.) with PT values of 1173.60 and 1260.48, respectively. Bromophos at 12 ppm failed to provide satisfactory protection to grain beyond 8 weeks.