Encarsia sp. is the main solitary endoparasitoid developing on the larvae of the cotton whitefly Bemisia tabaci (Gennadius), in western Burkina Faso. The biological control potential of this parasitoid is currently under investigation. Studies of some population parameters and biological control assays have been undertaken in the laboratory and greenhouse. Encarsia sp. can develop on the four larval stages of B. tabaci obtained in our study conditions, 7 to 15 days after oviposition. The highest rates of parasitism were recorded on the third and fourth larval stages of B. tabaci. The duration of Encarsia development was shorter on the third and fourth than on the first and second instars. The emergence rate of the F 1 generation was high (> 80%) and seemed not to be related to the different host stages. The sex-ratio favoured females (6: 1). Encarsia adults have a …