The initial and residual activity of KZ-oil, pyriproxyfen, imidacloprid, triazophos and cypermethrin were evaluated against whitefly infesting cotton plants during 2001 cotton season. Also, a treated-vial technique was used to bioassay insecticide susceptibility of whitefly populations in cotton fields. The tested chemicals could be arranged descendingly according to the general mean percent reduction in whitefly population as follows: imidacloprid, triazophos, KZ-oil, cypermethrin and pyriproxyfen. Tolerance ratios indicate the susceptibility of whitefly populations to KZ-oil and pyriproxyfen, while they were more resistant to the synthetic pyrethroid cypermethrin.