Laboratory evaluation of malathion, chlorpyrifos and chlorpyrifos-methyl for use against beetles infesting stored wheat

The relative toxicities of malathion; chlorpyrifos, 0,0-diethyl 0-(3,5,6-trichloro-2-pyridyl) phosphorothioate; and chlorpyrifos-methyl, 0,0 dimethyl 0-(3,5,6-trichloro-2-pyridyl) phosphorothioate to stored product beetles were determined using an impregnated filter paper technique. Chlorpyrifos-methyl was the most toxic compound to the 5 species tested and like chlorpyrifos was equally effective against malathion resistant and susceptible strains of Tribolium. On wheat of 12% moisture content chlorpyrifos-methyl was the most effective of the 3 compounds as a protectant against Sitophilus oryzae (L.).