The residual effect of five insecticides on Plutella xylostella (L) larvae was measured on Brassica rapa in the laboratory. Acephate was the most persistent and gave at least 80% larval mortality eight days after application. Bendiocarb, Bacillus thuringiensis, and methamidophos gave 50% larval mortality six days after treatment. Diflubenzuron demonstrated poor insecticidal activity – the larval mortality was 20% at all times.