Efficacy of a Bacillus sphaericus formulation as influenced by the qualityof Culex quinquefasciatus breeding waters

To understand the physico-chemical factors that influence the efficacy of B . sphaericus formulation in the breeding sites of Culex quinquefasciatus, a study was carried out in Mayiladuturai area of Tamil Nadu (India). The fac tors studied were hydrogen ion concentration (pH), acidity, alkalinity, chl orides, phosphates, total hardness, sulphates, total solids, dissolved soli ds, suspended solids, nitrate nitrogen, ammoniacal nitrogen, dissolved oxyg en, biological oxygen demand (BOD) and chemical oxygen demand (COD). Effica cy of the formulation was assessed in terms of reduction in larval populati on in the treated habitats. pH of water in the treated sites was around neu tral range (mean+/-SD 7.65+/-0.23). Phosphate content was low (2.27+/-1.34 ppm) whereas chlorides (326.1+/-55.8 ppm) and sulphates (38.9+/-23.8 ppm) w ere high. Total hardness ranged from 206 to 462.5 ppm with a mean of 312.1/-80.5 ppm. The chlorides and sulphates, though present in considerable qua ntity, did not have any influence on the efficacy of B. sphaericus formulat ion. However, the proportion of insoluble chlorides and sulphates which con tribute to total hardness seemed to influence the formulation adversely.