The plant tissue feeding of Anopheles sergentii Theobald, An. claviger Meigen, Culex pipiens Forskål and Aedes caspius Pallas (Diptera: Culicidae) was investigated. The relative frequency of plant feeding was compared to the general intake of sugar in different seasons and in different habitats in Israel. The study shows that mosquitoes feed on sugar-poor plant tissue in the lack of better options. Optimal conditions were in the sugar-rich En Fesha oasis, where plant tissue was found in only 0.3% of An. sergentii females, and, except for the winter, about 80% of females were sugar positive and the gut content was equivalent to 72.3 +/- 1.6 microg sucrose. By contrast, in the dry season in the desert, guts of 46.3% An. sergentii females contained plant tissue residues, only 46.0% were sugar positive, and the gut-content was less than a tenth, the equivalent of 5.6 +/- 0.9 microg sucrose. Age grouping of contemporary, desert An. sergentii showed that the growing population consisted mostly of newly emerged adults, as 80.2% of the females were nulliparous and only 12.1% of them survived one gonotrophic cycle.