Evaluation of the impact of bacillus thuringiensis israelensis and bacillus sphaericus on population dynamics of anopheles and culex mosquitoes in Mwea, Kenya
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Date
2012-04-20
Authors
Mutunga, Lucy Mumo
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Abstract
Insecticide resistance of malaria vectors has caused great concern in malaria vector management and has accelerated the search for alternative methods of vector management. Integrated vector management (IVM) targeting both the adult and immature stages have been adopted with renewed interest in larval management with the aim of making it cost effective. The possibilities that targeting species succession processes in the mosquito larval habitats like irrigated rice agro-ecosystem calls for research to evaluate microbial larvicides as potential tool to be incorporated in IVM programmes.
The population dynamics of the adult and larval mosquitoes in habitats within Mwea Irrigation Scheme and Mwea Irrigation and Agricultural Development centre (MIAD) was determined. A longitudinal study of20 experimental plots was set up and treated with three different types of larvicides (Bacillus thuringiensis israelensis (Bti), Bacillus sphaericus (Bs) and a combination of BtilBs) and observed for a period of 16. weeks during rice growth. Three villages representing planned (Munyaka), and unplanned rice cultivation (Kiamachiri and Murinduko) were also studied. Eight different mosquito species that included culicine and Anopheles mosquito species were morphologically identified. The Anopheles species in decreasing order included Anopheles gambiae (72.5%), Anopheles pharoensis (24.84%), Anopheles coustani (1.25%), Anopheles pretoriensis (1.25%) and Anopheles funestus (0.16%).
Among the culicines species, Culex quinquefasciatus (82.26%) were predominant followed by Culex poici/ipes (10.33%) and Culex anmdioris (7.41%). 'Anopheles gambiae, Culex quinquefasciatus and An. pharoensis occurred throughout the rice growth cycle, but their densities decreased each time after microbial larvicide application. The characteristics measured explained the vector density except for clear turbidity in the 3rd and 4th instars of Anopheles .., mosquitoes (P<0.05). Microbial larvicides reduced larval populations significantly (F . 3,536=7.56 p<O.OOOI). Negative binomial.regression showed Anopheles larval density to be significantly associated with habitat characteristics {P<0.005). Ditches had most Anopheles larvae with a mean of 0.82/dip (n=295) followed by pools 0.59/dip (n=99197) and seepage O.44/dip (n=373). Indoor adult mosquito collection through, Pyrethrum Spray Collection (PSC) showed that 97.01% (n=5780) of Anopheles gambiae and 2.83% (n=291) of An. funestus were the dominant species. These fmdings suggest that larvicidal application should target peridomestic habitats, paddies and associated canals between transplanting and tillering stages in order to achieve effective vector control.
Description
Department of Zoological Sciences,69p.The QR 82 .B3M8 2011
Keywords
Malaria vector management, Malaria --Biological control, Bacillus thuringiesis, Bacillus sphaericus