RESUMEN
The microbial larvicide, Bacillus sphaericus 1593, was evaluated against Culex quinquefasciatus larvae in artificial pools at Huay Kwang area in Bangkok between March and October 1985. This study was aimed at determining the residual activity of B. sphaericus 1593 in waste water under field conditions. The larvicidal activity of B. sphaericus 1593 was found to persist for at least 5 months in artificial pools containing waste water. The populations of B. sphaericus 1593 in the test water fluctuated, decreasing by approximately 4.25 and 3.47 log10 colony forming unit (cfu)/ml from the original concentrations in 60 and 80 days after application and then increasing approximately 2.92 and 2.77 log10 cfu/ml in 92 and 72 days for pools No. 1 and No. 2, respectively. This evidence indicates that B. sphaericus 1593 can recycle in such conditions.