Efficacy of a granular formulation of Bacillus sphaericus against Culex quinquefasciatus and Anopheles gambiae in West African countries.

The efficacy of a sustained released granular formulation of Bacillus sphaericus strain 2362 was compared to a flowable concentrate in containers, cesspools, and water ponds. Duration of control was dependent on formulation, dosage, exposure to sun, site, recycling, and target mosquito larvae. In a series of container tests with repeated additions of fourth-instar Culex quinquefasciatus larvae exposed to 0.3 or 3.0 g/m2 when cadavers were not removed, more than 95 percent control was obtained for two and four days in containers that were exposed to the sun with sewage water treated with the flowable concentrate compared to four and seven days for those treated with the granule. In sun-exposed containers with sewage water, control persisted for two days for the flowable concentrate at both dosages and one and six days for the granule at 0.3 g/m2 and 3.0 g/m2, respectively. Compared to the above tests, more than seven weeks control was obtained with 0.3 g/m2 of the flowable concentrate in closed containers where larvae were added weekly. In closed containers without weekly addition of larvae, the control was 15 percent when larvae were added five weeks after the treatment. Spore counts at the surface and bottom of the containers with lids showed an increase in number of spores at the surface where larvae were added weekly and a rapid decline where they were not. Spore counts at the bottom showed settling in both cases, but to a much higher level where larvae were added weekly. Nearly 100 percent control of Cx, quinquefasciatus larvae was obtained for at least 16 days in cesspools in Yaoundé, Cameroon, treated with the granule at 3.0 g/m2 compared to approximately nine days for the flowable concentrate. At 0.3 g/m2, the duration of this reduction was five days for both products. Nearly 100 percent control of Anopheles gambiae was obtained in sun-exposed water ponds near the village Kotiokh, Senegal, for at least 15 days with the granule at 3.0 g/m2 compared to just five days for the flowable concentrate at the same dosage.