WHO-approved insecticides were co-intercalated with hexadecyl-trimethylammonium (HDTMA) chloride in bentonite in an attempt to improve their persistence. XRD and FTIR confirmed successful co-intercalation of the insecticides. Bioassays revealed that the activity of co-intercalated insecticides deteriorated after just one week of accelerated aging at 40 degrees C and 90% RH. However, when the pH of the bentonite slurry used for intercalation was reduced with acetic acid to pH = 4.5, the persistence life increased to 113 days. The performance ranking with respect to both knockdown and mortality was as follows: Co-intercalated alpha-cypermethrin > co-intercalated propoxur > co-intercalated DDT > DDT.