Some Mosquitos of the Blue Nile Valley in the Republic of the Sudan

The rainfall of the Blue Nile valley diminishes towards the north, and the number of mosquitos tends to do the same, but the natural state of affairs has been somewhat altered by irrigation works in the shape of the Sennar reservoir and the watering of cotton, sorghum and sunt trees (Acacia arabica, Willdenow), and will be further altered when the proposed dam at Roseires is constructed.The latter dam will form a large reservoir in the Kiri-Roseires area where conditions are likely to differ from those of the Sennar reservoir. Anopheles funestus Giles and many other species occurred in the stretch downstream between Roseires and Abu Hugar in which riverside basins, overgrown with sunt trees, were flooded when the river was high.Farther downstream, between Karkoj and Sennar, breeding conditions were affected by the Sennar dam, water at full storage level reaching different heights in the basins according to their distance from Sennar. Near Sennar the dualpurpose dam had a particular effect on the aquatic vegetation and the mosquitos.A. gambiae Giles bred among Najas pectinata (Parl.) Magnus which, however, only occupied a small area in the reservoir, A. rufipes (Gough) bred in small numbers in various places, and A. pharoensis Theo. in a large area of creeping grass growing on silt under conditions which caused it to form a raft that rose and fell with the water. Adults of A. pharoensis, which was by far the commonest Anopheline, rested near houses by day at certain times of the year. Control of the grass was difficult and liable, to favour more dangerous species of mosquitos. Differences between the Sennar and Jebel Auliya reservoirs are discussed.In the riverain area between Abu Geili and Soba, A. gambiae bred in residual pools in the river-bed in the dry season and in flooded sunt basins in the rains. Control of larvae was very difficult in these basins and much reliance was placed on residual sprays against adults in houses.Breeding conditions in the Gezira irrigated area are described with particular reference to the type of clay soil. There were many larvae of A. gambiae in field channels at the end of the rains when irrigation began, and in March when the summer started. The latter increase was not reflected by any increase in the number of adults, probably owing to the reduction in length of life of the latter in the very hot dry weather. A. rufipes was sometimes found in houses. Control measures are briefly described.Some mosquitos of Khartoum and a few other areas within the Blue Nile valley are briefly considered.