An assessment of the use of formulations of the microbial agents Bacillus thuringiensis and Bacillus sphaericus in the control of larvae of mosquitoes that cause malaria and filarial diseases

Two biological formulations of microbial agents Bacillus thuringiensis and Bacillus sphaericus known by their trade names as Vectobac 12 AS and VectoLex CG (Corn Cob) granules, respectively were obtained from Abbott Laboratories of North Chicago, USA. The B. sphaericus formulation was used in trials against Culex mosquito larvae in choked gutters at Labadi, Ashaiman and Nungua in the Greater Accra Region, whilst the B. thuringiensis formulation was used against Anopheles sp. in paddy rice fields at Akuse. The results indicate a 99 to 100% mortality of all larvae with both B. thuringiensis and B. sphaericus for 5 to 16 days after applying the formulations at the breeding sites. Only small quantities of the products were needed to kill hundreds of larvae within 24 to 48 h. The formulations act on filterfeeding and grazing aquatic insect larvae after ingestion. They do not affect non-target aquatic insects and they are entirely harmless to humans. In this report, larvicide control using bio-larvicides has been proposed as one reliable method of reducing disease prevalence by killing the larvae at their breeding sites thus interrupting the life cycle of the mosquito vector at the larval stage.