A field trial of expanded polystyrene balls for the control of Culex mosquitoes breeding in pit latrines.

wHo 1984). Mosquito-infested latrines present a difficult control problem. Conventional methods, using insecticides or larvicidal oils, have given good results, but are expensive, require frequent application on a routine basis, and may be hampered by problems of resistance (World Health Organization 1984). As an alternative, Reiter (1978) suggested that a layer of expanded polystyrene balls (EPB) could be used as a floating "blanket" to prevent mosquitoes from breeding in these sites. Recent field-trials of the idea have given encouraging results in Tanzania and Kenya (Curtis and Minjas 1985) and in Zimbabwe (Morgan and Mara 1982). In this note I report on a small trial which I conducted in Kisumu, Kenya, in 1977. The trial area included low-lying parts of the Nyalenda and Nyamasaria neighborhoods of Kisumu (0" 06'5, 34" 45' E), on the shores of Lake Nyanza (formerly Lake Victoria). During the rainy season, the water table in these districts is higher than the bottom of many of the latrine pits, providing ideal conditions for Cx. quinquefasciatus and other sewage-breeding