[Campaign against Culex quinquefasciatus using Bacillus sphaericus: results of a pilot project in a large urban area of equatorial Africa].

Culex quinquefasciatus, which is sometimes the vector of Bancroft's filariasis, is a harmful mosquito, the immature stages of which live in collections of waste water resulting from human activity. Larval control, the most appropriate method, is at present carried out with chemical insecticides. But the toxicity of these compounds, together with phenomena of resistance, and the cost of substitute insecticides have turned research towards products of biological origin, and one of the most promising is a liquid concentrate of Bacillus sphaericus strain 2362. This was applied experimentally over an area of 200 hectares in a large city in the south of Cameroon, characterized by a short dry season during which mosquito density is at its highest. Spraying was carried out every three months for a year in a concentration of 10 g/m2 and its efficacy evaluated at the level of adult mosquitos through an indirect system of capture on human baits. The results of this study show, in essence, a reduction by 52.7% in the number of females captured in the overall study area treated, and that the impact of treatment is greater during the period of high mosquito density (55.1%) than in the low density period (40.7%). After analysis of the full set of results, the authors conclude that the pattern of rainfall, the conditions in which the insecticide is applied and reinvasions of mosquitos from untreated areas were the principal factors limiting the efficacy of this control campaign.(ABSTRACT TRUNCATED AT 250 WORDS)