Investigations into the Ecological Determinants of Distribution of Anopheles Gambiae S.S. (Diptera: Culicidae) Larval Populations in Urban Accra, Ghana

Abstract

Anopheles gambiae s.s. larval habitats are important determinants of adult distribution and abundance, which also determine the geographical pattern of malaria disease. Information on their habitat characteristics can contribute greatly to a better planning of its control strategies through environmental management. To identify the environmental parameters, which influence the distribution of An. gambiae s.s. larval populations in urban Accra, Ghana, 30 habitats with An. gambiae s.I. and 24 without but with other mosquito species were studied Mosquito larvae and pupae were collected and reared to adults Water samples were taken at the same time of mosquito collection for physico-chemical analyses. The adult mosquitoes obtained were morphologically separated into An. gambiae s.I. and other species and counted. Then PCR-based methods were used on 300 mosquitoes to identify the members of An. gambiae s.I. and for microsatellite DNA analyses of An. gambiae s.s. AGXH7 locus using published oligonucleotide rnicrosatellite primers. The microsatellite DNA data generated was used to determine the population structure and construct the phylogenetic relationships between An. Gambiae s.s. populations. Twenty-eight physico-chemical parameters of each water sample were measured and those that on comparison were found to be significant were analysed further using linear discriminant function analysis and multiple regression analysis to reveal the best predictors of present o or absence, and abundance of An. gambiae s.s. in habitats. Then hierarchical cluster analysis using these water parameters was performed to reveal similar habitats, which was then compared with molecular phylogeny obtained. All the 300 An. gambiae s I. were Klenlified as An. gambiae s.s. Turbidity, pH and calcium wore found to be the most significant discriminatory parameters associated with the presence or absence of (he An. gambiae s.s. in the habitats and were also selected as the best predictors of larval abundance. It was also observed that the molecular phylogeny of An. gambiae s s populations that bred alone in habitats fitted exactly with the clustering obtained using their water parameters. Also, closer populations were more likely to have relatively similar values of turbidity, pH and calcium concentrations and were also more likely to have similar allelic and genotypic frequencies.