Impact of Slow-Release Bacillus sphaericus Granules on Mosquito Populations Followed in a Tropical Urban Environment

A floating, slow-release, granular formulation of Bacillus,sphaericus (Neide) Was used to control mosquito larvae in two suburban areas of two tropical cities: Ouagadougou and Bobo-Dioulasso, Burkina Faso. A circular area of 2 km(2), diameter 1,600 m, was treated in each city using a similar, smaller area 1 km away as an untreated control. Mosquito captures were made in houses in four concentric circles, from the periphery to the center each circle was 50 in in width. Mosquitoes were captured in CDC light traps or from human landings. More than 95% of the mosquitoes were Culex quinquefasciatus (Say) (Diptera: Culicidae). The human landing catches provided twice as many mosquitoes as did the CDC traps/ night/house. The treatments resulted ill important reductions relative to the control area and to preintervention captures. The reduction was more prominent in the inner circle (tip to 90%) than in the outer circle (50-70%), presumably because of the impact of immigrating mosquitoes from nontreated breeding sites around the intervention area. This effect was more pronounced for light trap catches than from, human landings. The impact of treatment was also measured its the mean ratio of mosquito density in the two outer circles to that of the two inner circles. This ratio was similar to 1:1 before the intervention and reached 1:0.43 during the intervention, This comparison does not depend oil the assumption that, in the absence of intervention, the mosquito population development in the two areas would have been identical, but does depend oil the homogeneity of the intervention area. The study showed that it is possible to organize mosquito control in a tropical, urban environment by forming and rapidly training teams of young people to carry out the mosquito control mostly using a biopesticide that call be applied without any tools except an iron bar to lift lids oil some cesspits.