Effects of bacillus thuringiensis var.Israelensis and Bacillus Sphaericus larvicides,on mosquitoe Abundance, Diversity and Distribution in Selected Areas of lusaka urban district,Zambia
Date
2013-04-15
Authors
Kandyata, Alister
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Abstract
Effects of Bacillus thuringiensis var. israelensis (Bti) and Bacillus sphaericus (Bs) biolarvicides, on mosquito abundance, diversity and distribution in selected areas of Lusaka urban district, Zambia, were investigated. Four study areas including parts of the dam/stream systems of the Kalikiliki/Ibex hills area; Venta/Manzi valley area; Chelstone-Zambia airways marshy ponds area, and the Chamba valley brick factory area were selected, based on their being parts of areas where the Larval Source Management (LSM) programme using Bti and Bs was being implemented by the Ministry of Health in the district.
The study hypothesised that the anopheline mosquito species, Anopheles gambiae sensu stricto, was the dominant vector of malaria in Lusaka urban district; LSM using Bti and Bs reduced the abundance and diversity of anopheline mosquito larvae in their breeding sites; and that the use of Bti and Bs affected anopheline mosquito species distribution. Study Specific objectives were to: assess the ratio of mosquito colonised habitats to potentially available habitats in the study areas before and after larviciding; identify species of mosquito larvae and adults present in the study areas before and after larviciding; assess mosquito abundance, diversity, distribution patterns and species dominance in the study areas before and after larviciding; and to compare incidences of malaria prior to and after the larviciding programme in the study areas.
Biolarvicides (Bti and Bs) were sprayed on freshwater bodies in the study areas in June and July, 2011 using Hudson X-pert pressure pumps and a fixed-wing, single-engine aircraft. Incidences of malaria prior to and after larviciding were determined by reviewing and analysing health facility records of positive malaria cases attended to by health facilities in the study areas.
None of the major malaria vectors reported for Zambia in the literature from the Anopheles gambiae sensu lato (s.l) or the An. funestus s.l were identified from the study areas. Instead three anopheline mosquito species; Anopheles coustani Laveran, An. squamosus Theobald and An. rufipes Gough, were found in the study areas. Anopheles coustani (13.5%) and An. squamosus (9.5%) were collected from all four study areas, while An. rufipes (1.1%) was only found in one study area. Prior to larviciding, culicine mosquito larvae were the most abundant (75.9%) in the study areas. No Culicidae larvae of any species were found in the freshwater bodies after larviciding. Possible reasons for the absence of known major malaria vectors from the study areas are suggested. The potential of biolarviciding as malaria vector control intervention for integration with Indoor Residual Spraying (IRS) and Insecticide Treated bed Nets (ITNs) are discussed. Incidences of malaria were higher prior to larviciding (2-17%). Positive malaria cases dropped drastically, after larviciding (2-4%), in all four study areas. However, though numerically very small, percent-wise, rises in malaria positive rates, were observed in Chainda area by second month post-larviciding but continued declining in the other areas. Possible reasons for the slight rise in the incidences of malaria were due to case importation. This study recommended the integration of Bti and Bs LSM into the Malaria Control Programme in Zambia.
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Keywords
Mosquitoes-- control--Zambia , bacillus thuringiensis , Bacillus Sphaericus