AbstractWettable powder formulations of the organophosphorus insecticides, fenitrothion and pirimiphos‐methyl, and the pyrethroids, permethrin and deltamethrin, have been compared for persistence and activity on woven polypropylene fabric; the residues produced in maize kept under the test sheets have also been measured. The test insects wereSitophilus oryzue(L.) andTribolium custuneum(Herbst). Permethrin at 41 and 83 mg m−2was completely effective for the full 12 weeks of the experiment. Deltamethrin at 6.2 and 12.5 mg m−2was almost equally effective but after 4 weeks the deposit was slower acting againstS. oryzae. The organophosphorus compounds were effective only up to 2 weeks at 250 mg m−2and up to 4 weeks at 500 mg m−2. No residues could be detected under the pyrethroids but the organophosphorus insecticides gave residues of 2–4 mg kg−1on a thin layer of grain. This residue was biologically effective against the