We investigated the role of an entomogenic gut bacterium Pseudomonas fluorescens on larval development and survival of Culex vishnui Theobald, the mosquito vector of Japanese encephalitis, which breeds exclusively in rice field water in tropical regions. The bacterium could be isolated from the midguts of third and fourth instars of the mosquito. Pseudomonas fluorescens strain 1 (Ps1) was identified as the one vital to C. vishnui larval survival. The phenotypic characteristics of this strain are described. As part of the study, antibiotics were used to cure C. vishnui larvae of Ps1; thus cured larvae did not survive when subsequently reared in sterile or antibiotic-treated rice field water or tap water. In contrast, 93.3–100% of cured larvae developed into normal adults when subsequently reared either in unsterile or in sterile rice field water or in tap water containing Ps1 bacteria (5 × 103 ml). Thus the elimination of Ps1 from breeding water could be used as a strategy to suppress the mosquito growth, as part of an innovative approach to control Japanese encephalitis.
