Lethal and sublethal effects of two commonly used defoliants, Def and Dropp, on whitefly, Bemisia argentifolii, and its parasitoids, Eretmocerus eremicus and Eretmocerus hyati, were evaluated in laboratory and greenhouse tests. Whitefly eggs and adults were more susceptible to defoliant treatments than larvae. The reduction in feeding sites differentially affected whitefly nymph mortality depending on instar. Sublethal effects of Def, Dropp or their mixture on whitefly were manifested through reduction of percentage female progeny and the number of eggs deposited per female per day after spraying young nymphs. The timing of application significantly affected parasitoid survival. After defoliant treatments of whitefly nymphs parasitized with early instar E. eremicus larvae, the number of parasitoid female progeny was significantly reduced and their longevity was significantly shorter than those of controls.