FIELD TRIALS WITH BACILLUS-SPHAERICUS FORMULATIONS AGAINST POLLUTED WATER MOSQUITOS IN A SUBURBAN AREA OF BANGKOK, THAILAND

Two newly developed Bacillus sphaericus larvicidal formulations, Vecto Lex CG(R) (corncob granules) and VectoLex WDG(R) (water dispersible gr anules), were tested against Culex quinquefasciatus larvae in 4 highly polluted breeding sites in Thailand. VectoLex CG, applied at rates of 0.5-2 g/m(2), gave satisfactory to complete control of late-instar la rvae and pupae for up to 4 wk after treatment. The VectoLex WDG, which had higher potency and was applied at rates of 0.1-0.5 g/m(2), gave s atisfactory control for 1-4 wk after treatment. Among the factors infl uencing longevity of control were dosage of a given formulation, preci pitation, and flooding of the treated sites; the latter had the greate st impact. Presence of larvivorous fish did not seem to influence larv al populations because there were heavy populations of mosquito larvae present in the test sites in the presence of moderate numbers of fish before the application of B. sphaericus treatments.