Dialeurodes citri (Ashmead) and Parabemisia myricae (Kuwana) have become the most serious citrus pests in the Mediterranean region of Turkey since 1976 and 1983 resp. The main characteristics in morphology and biology by which they can be distinguished are compiled. D. citri is larger but passes only 2-3 generations per year and is confined to fully developed leaves. P. myricae appears earlier in spring, passes 7-8 generations and prefers the very youngest, not yet unfolded leaves, but also occupying fully expanded leaves and thereby restricting the potential breeding sites of D. citri. It replaces, therefore, D. citri in those areas in which both species meet. The damaged produced by both species consists of removal of assimilates and the copious production of honey dew which stimulates the growth of sooty molds. In southern Turkey 16 host plant species of D. citri and 26 host plant species of P. myricae have been found. Both species thrive best in dense citrus stands with high humidity. They are attacked by a number of indigenous predators which have, however, only a minor impact on their population dynamics. D. citri can be controlled by cultural methods - wide-space planting and thorough pruning - and by white oil sprays. These measures are not sufficient to suppress P. myricae, but biological control with the introduced aphelinid Eretmocerus de Bachi (Rose) has proved to be a complete success.