The residual concentration and efficacy of Abate 5CG (impregnated in celatom granules) and plaster pellets impregnated with either Abate 4E or technical temephos were compared against late 3rd-instar Aedes aegypti larvae. Both plaster pellet formulations resulted in 100% larval mortality during the 6-wk test, compared with 2 wk for a similar level of mortality for the celatom formulation. The maximum temephos concentration in water treated with the celatom formulation occurred 30 min after treatment at 0.071 ppm. Temephos concentration of water treated with the 4E plaster formulation peaked at 12 h at 0.148 ppm while the concentration of the technical plaster formulation peaked at 48 h at 0.30 ppm.