EFFICACY OF LONG-LASTING MICROBIAL LARVICIDES ON MALARIA VECTORS IN DIFFERENT ECOSYSTEMS IN WESTERN KENYA SAMUEL KAHINDI

Abstract

Malaria remains a major health challenge in Kenya despite implementation of various intervention strategies to overcome the burden. Chemical-based vector control interventions are threatened by development of insecticide resistance and changes in vectors behavior. This study was designed to evaluate the efficacy and persistence of long-lasting microbial larvicides formualtions (LL3 and Fourstar briquets) consisting of Bacillus thuringiensis variety israelensis (Bti) and Bacillus sphaericus (Bs) in different ecosystems in western Kenya. Two briquet formulations of Bti/Bs (namely LL3 and Fourstar) were evaluated against anopheleine larvae under lab, semi-field and field conditions. During laboratory and semi-field evaluations, two larvicide solutions as well as control solution were prepared and tested for efficacy against Anopheles mosquito larvae. Field evaluation of the two larvicides was done in irrigated (Ahero irrigation scheme) and non-irrrigated (western Kenya highlands) ecosystmens with diverse habitats. Larval habitats were monitored for mosquito larvae using the standard dipping technique for 30 days pre and 5 months post-treatment. Evaluations for the irrigated ecosystem larvicidal effect was assessed for 12 weeks using mosquito emergent traps placed in each of experimental rice paddy. Results in both laboratory and semi-field conditions showed both larvicide solutions had larval mortality of 90% and no pupation occurred within 60 days. There was no significant difference in the efficacy of the two larvicide solutions in both lab and seni-field conditions (GEE, P < 0.05). In the non-irrigated ecosystems, the overall larval density in treatment habitats was significantly reduced (GEE, P < 0.05) as compared to the control habitats. Larval mortality varied significantly with habitat type with a higher reduction in Anopheles larval density observed in the abandoned goldmines, while drainage canals had the lowest reduction. The two larvicides significantly reduced vi emerging anophleine mosquitoes in the irigated rice ecosystmems resulting in 78% and 70% reduction respectively. The LL3 and FourStar® briquettes larvicides proved effective in reducing larval population and adult emergence in Anopheles mosquitoes for a prolonged duration of above three months. However, there is need to integrate these long-lasting microbial larvicides with the existing tools for malaria vector control for significant reduction in malaria transmission. Key words; Anopheles gambiae, An. funestus, Bacillus thuringiensis var israelensis and B. sphaericus LL3, Fourstar