Evaluation Of Bacillus Thuringiensis Var Israelensis And Bacillus Sphaericus Briquets As Anopheles Mosquito Larvicides In Vihiga County, Western Kenya

ABSTRACT

Malaria is a key hindrance to the improvement of health in tropical and subtropical countries of the world with more than two billion people exposed to it. One of the approaches of controlling vectors of malaria is by targeting aquatic stages at source. This would lead to significant reduction in the adult vectors as well as malaria transmission. Entomopathogenic bacteria Bacillus thuriengiensis var israelensis (Bti) and Bacillus sphaericus (Bs) in the form of dispersable granular form has been one of the ways of managing malaria. This approach has had a number of drawbacks such as having short residual life span which increases treatment frequency leading to more labour cost. Moreover most are less effective since they have only one active ingredient of either Bti or Bs. Therefore, formulation of dispensing the entomopathogen in solid form would enhance slow release of insecticidal residue over a long period of time. This research set out to determine the impact of a new solid FourStar briquets formulation on aquatic Anophiline larval stages in Kenya. In addition, the study investigated the duration of briquets applied in the mosquito breeding larval sites. The effectiveness of FourStar briquet in identified selected three zones habitat was done within 180 days at Emakakha Location, Emuhaya sub-county in Vihiga County. Larvae and pupae after being sampled were picked from the tray by use of a pipette. The larvae were counted for ten dips at each of the ten identified mapped larval sites per the six habitat sectors. The post treatment was done after applying the 30 grams FourStar briquets as recommended by FourStar Microbial LLC company at a rate of one briquet of 30grams per nine square metres of water surface area on the identified zones sectors. A weekly post treatment data of mosquito larvae abundance was recorded in larval distribution survey forms in each larval site. The differences in the abundance between the control and intervention among the two mosquito species of Anopheles gambiae and Anopheles funestus were compared using student t-test. The correlation between mean numbers of Anopheles gambiae and Anopheles funestus collected in treated sites over time was calculated. All these analyses were carried out using the Statistical Package for Social Scientists (SPSS for windows version 20.0). In the three field treated larval habitat sites, larval productivity of Anopheles gambiae were greatly reduced by 100% for the first two months and 98- 80% after third to sixth months. The results obtained indicated that there was significant difference among Anopheles gambiae larvae (P=0.021). This showed that Anopheles gambiae larvae are highly susceptible to the FourStar briquets. The briquets were effective and reduced Anopheles funestus larval productivity by 100% in the first two months and 99-87% after third to sixth months. Significant difference on early stages of Anopheles funestus was (P=0.032). Correlation between the mean numbers in treated larval sites over time Anopheles gambiae was significant (P=0.001) while Anopheles funestus was also significant at P=0.001. The larvicide reduced Anopheles larval abundance among the two Anopheline larvae instars significantly. The results of this study demonstrate the potential of using the solid briquette as a strategy to reduction of adult mosquito vectors as well as malaria transmission in Western Kenya Highlands.