Mosquitoes and malaria transmission in irrigated rice-fields in the Benoue valley of northern Cameroon.

Africa has a very high human population growth rate which is not matched by the rate of increase in agricultural production per capita. One solution often envisaged is to increase of the area of irrigated land, permitting two crops per year. The most extensively irrigated crop is rice, for which demand continues to increase. Rice-fields are usually flooded for long periods, providing suitable breeding places for mosquitoes. Everywhere in tropical Africa, rice-growing areas allow considerable multiplication of malaria vectors of the Anopheles gumbiue complex (Service, 1989; Lacey and Lacey, 1990). ' . In the North Province of Cameroon, it has been well established that the largescale irrigation development following the Lagdo dam has resulted in increasing human malaria incidence (Slootweg and Schooten, 1990). This note describes a preliminary entomological study carried in 1990 in the village of Gounougou. Gounougou is located 40 km south-east of Garoua on the right bank of the Benoue river, immediately downstream of the Lagdo barrage. The region belongs to Sudan savanna zone, having a distinct rainy season from May to October with a total annual rainfall of 1000 mm. In the dry season (November-April) rainfall is very rare. The majority of the immigrant population of Gounougou settled between 1978 and 1985, during the construction of the Lagdo dam and the subsequent irrigation scheme. Irrigated rice-culture commenced in 1987 over 50 ha; in 1988 another 30 ha of rice and 80 ha of a variety of crops was added. At present some 800 ha for rice and other crops are under grading around the nearby villages of