Impact of a 26-month Bacillus sphaericus trial on the preimaginal density of Culex quinquefasciatus in an urban area of Recife, Brazil

A field trial using the entomopathogen Bacillus sphaericus against Culex qu inquefasciatus was conducted in a district of Recife, Brazil, an area with a high prevalence of lymphatic filariasis. In this urban area more than 2,5 00 Cx. quinquefasciatus breeding sites within a 1.2-km(2) area were found a nd subsequently submitted to a long-term treatment with B. sphaericus. To e valuate the impact of treatment on the densities of Cx. quinquefasciatus pr eimaginal forms, 26 breeding sites, representative of the major site types found in that area, were monitored for 3 years. Parameters such as mean and maximum densities of larval population as well as the frequency of infeste d sites were recorded before, during, and after the trial. The level of eac h parameter was greatly reduced during the treatment period, particularly i n the 2nd treatment year. A low density of Cx. quinquefasciatus was also ma intained throughout the last year, in the absence of treatment. Analysis of the data reported here confirms B. sphaericus as a very effective larvicid e against Cx. quinquefasciatus despite the optimal environmental conditions for mosquito proliferation in the urban area of Recife.