Phlebotomus papatasi, the vector of Leishmania major in arid foci in the Jordan valley, obtains carbohydrates by feeding on plants and the sources were identified. At the end of the dry summer when the fly population was the highest, only a small proportion of them had plant tissue residues (cellulose particles) or sugar in the gut. The life span of the flies was very short and this allows only a small proportion of flies to complete a gonotrophic cycle or transmit L. major. In the dry season the plants are under heat and dehydration stress that arrests the photosynthesis and reduces the amounts of the main end products in leaves, sucrose and starch. We presumed that the paucity of sugar in the sand fly diet resulted from the arrest of photosynthesis. This assumption was supported by the comparison of sand fly feeding on Capparis spinosa (caper plant) branches that had been kept for 24 hrs in darkness and on branches that had been cut after a normal day of photosynthesis. In darkness the branches had lost more than a half of their sugar contents, the proportion of flies that fed on them decreased by a half and the ingested meals were much smaller. Laboratory experiments also showed that plant-feeding sand flies often ingest starch grains and such grains were also found in a high proportion of field caught flies. Alpha-amylase activity that was found in Ph. papatasi and in L. major promastigotes indicated that starch could be utilized by both. Sand fly plant-tissue meals also include cellulosic cell-wall residues however, only the parasites possess a cellulase enzyme complex. Thus, the ingested cellulose is degraded and utilized only in Leishmania infected flies. Another aspect of the plant feeding is the agglutination and killing of L. major promastigotes in the gut of infected flies, by the ingested tissues of some plants. Inhibition of these effects by sugars, in experiments with cultured parasites and plant extracts, indicated that the parasite death was caused in most cases by lectins. The cytotoxicity of Solanum sp. was apparently caused by solanaceous alkaloids since the effect of the plant extract was not inhibited by sugars. In addition to their effect on the parasites the feeding on some plants was deleterious to the sand flies and compared to controls, a single meal could shorten their median survival by more than a half.

Index terms: Phlebotomus papatasi, Leishmania major, photosynthesis, lectins.

Acknowledgments: This study was supported by NIH grant RO1 Ai40926, the Center for the Study of Emerging Diseases and Deutsche Forschungsgemeinschaft

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