An assessment of microbial formulations of Bacillus thuringiensis and Bacillus sphaericus for the management of mosquito larvae causing malaria and filariasis

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 Culexmosquito larvae in choked gutters at Labadi, Ashaiman and Nungua in the Greater Accra Region, whilst the B. thuringiensis formulation was used against Anophelessp. 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 application at their breeding sites. Both the products tested are effective to kill the target larvae at 24 to 48 h even at low concentrations. The formulations act on filter-feeding and grazing aquatic insect larvae after ingestion. They do not affect non-target aquatic insects and are harmless to humans. In this report, mosquito 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 at the larval stage.   Key words: Mosquito, larvae, formulations, breeding site.