Experimental formulations of Bacillus sphaericus and B. thuringiensis israelensis against Culex quinquefasciatus and Anopheles gambiae (Diptera: Culicidae) in Burkina Faso

Efficacies of locally produced, sustained release granular formulations of Bacillus sphaericus (BS) strain 2362 and B. thuringiensis israelensis (BTI) were compared with commercial liquid concentrates of the same bacteria in cesspits and rain-filled puddles in Ouagadougou, Burkina Faso. Duration of control was dependent on the product, the transient nature of some sites, and the target mosquito larvae. BS granules applied at the rate of 3.0 g/m2 (30 kg/ha) reduced Culex quinquefasciatus Say 99% for at least 28 d in cesspits, whereas the same dosage of 2 BTI granules and commercial liquid formulations of BS and BTI gave 95% control for 8-14 d. The levels of control obtained with the 2 liquid products were not different. Accordingly, the reported inferiority of BTI to BS in polluted water was attributed to low dosages of BTI. Because products were compared at equal application rates, recycling seemed to play a minor role compared with product formulation. BTI was more broad spectrumed than BS also killing Cx decens Theobald, Cx cinereus Granpré & Charmoy, and psychodid larvae. Depending on the method of estimation, granular and liquid BS gave 60-97% control of Anopheles gambiae s.l. Giles for 10 d in rain puddles. The transient nature of the rain puddles was probably more important for the duration of control than formulation type. Cesspits and puddles, respectively, were the most important larval habitats for these 2 species in Ouagadougou during the rainy season, and these trials showed that An. gambiae was not controlled easily with larvicides alone. However, biological larvicides may play a central role in the control of Cx. quinquefasciatus provided that most breeding sites are treated.