Observations on the Anopheles gambiae complex in the Senegal River Basin, West Africa.

ABSTRACT. 1. Three sibling species of mosquitoes of the Anopheles gambiae complex are found in the Senegal River Basin: An.melas Theobald,A n.gambiaeG iles and An.arabiensisP atton. 2. An.melas is restricted to the river delta and environs where saltwater breeding places are present. 3. An.gambiae and An.arabiensl,sa re sympatric in the study area; An.arabiensis predominates in coastal zones where it breeds also during the dry season;A n.gambiaep redominatesi n inland areasw here breeding is mostly restricted to the rainy season (July-September). 4. An.arabiensis is chromosomally polymorphic all over the study area, with much variation of inversion frequencies, particularly for the 2Ra arrangement. 5. An.gambiaei s characterizedb y a very high frequencyo f the2Ptb-2La inversion arrangement which is typical of the Savanna chromosomal form