The gregarious phase of the Desert Locust, Schistocerca gregaria (Forsk., 1775), is known for a long time for its great polyphagia and the broad variety of crops attacked. Polyphagia seems more limited in the solitary phase whose diet is largely unknown. This work, conducted in the Algerian Sahara, deals with the qualitative and quantitative assessment of the diet of solitarious Desert Locust. The qualitative assessment of the diet was made by comparing the range of plant species in the locust biotopes with plant species identified in the faeces. The quantitative assessment was realized by comparing the frequencies of plant species observed in the faeces with their abundances in the field. The frequency of plant species consumed could be estimated by the ratio of imagos which have consumed the plant species on the number of imagos present in the biotope. The discrepancy observed between the plant species eaten and their abundances in the habitats shows a strict food selection. It appears that the diet of the Desert Locust depends on both the floristic composition of the vegetation and of the choices he made in his search for food. The food spectrum of the adult is extended to the species not very abundant and far from abundant. The adult displacement increases the probability of a widened choice. In general, the plants appreciated by the Desert Locust are those which allow the best development and reproduction. (Texte intégral)