Phlebotomus papatasi (Scopoli), the vector of Leishmania major (Yakimoff & Schokhor), feeds on plants in desert habitats in the Jordan Valley. At the end of the dry summer, the life span of sand flies is short and the amount of sugars in their guts is small. In this season the plants are under the stress of heat and dehydration. This stress arrests the photosynthesis and decreases the amounts of the main end products, sucrose and starch. We presumed that the paucity of sugars in the sand fly plant tissue diet resulted from the arrest of photosynthesis. To test this assumption, we compared the feeding of sand flies on branches of Capparis spinosa (L.) that had been kept for 24 h in darkness and on branches cut after a normal day of photosynthesis. In darkness, the branches had lost more than half of their sugar content. Afterward they were fed upon overnight by 45.2% of female and 14.3% of male sand flies. A higher proportion of 81.0% females and 38.7% males fed on branches from natural conditions and these fed flies were significantly heavier. Laboratory experiments also showed that plant tissue meals of P. papatasi often include starch grains. Such grains were found also in 50% of field-caught males and females. The nutritive potential of plant tissues was demonstrated by the 33-d median survival of P. papatasi series that had been maintained on fresh C. spinosa branches and water.