Gichuki, Deborah Wangechi2025-08-132025-08-132025-06https://ir-library.ku.ac.ke/handle/123456789/31198A Thesis Submitted In Partial Fulfillment of the Requirements for the Award of the Degree of Master of Arts in International Relations and Diplomacy in the School of Law, Arts and Social Sciences of Kenyatta University, April 2025. Supervisor 1. James Nonoh 2. Sauda Swaleh 3. Regina NtaboMalaria remains a signifianct global health challenge, with Africa bearing a disproportionate burden. In Kenya, Anopheles arabiensis has emerged as a key malaria vector, particularly in coastal regions, following shifts in vector dynamics due to control measures. While bacteria in oviposition sites are known to influence mosquito egg-laying choices, the precise roles of these microbial communities in attracting or repelling An. arabiensis are not fully elucidated. This study aimed to characterize physicochemical parameters and bacterial communities in preferred and non-preferred oviposition sites of An. arabiensis in Kwale County, Kenya, and to evaluate the role of these bacteria in mediating oviposition. The study had three objectives: (i) To determine the physicochemical characteristics of Anopheles arabiensis larval habitats; (ii) To identify bacterial profiles in oviposition sites of Anopheles arabiensis in malaria-endemic regions of Kwale County; and (iii) To evaluate the role of bacterial communities in attracting Anopheles arabiensis mosquitoes to oviposition sites. The study identified distinct larval habitats, with preferred sites exhibiting significantly higher An. arabiensis larval densities (M >10 larvae/dip) compared to non-preferred sites (M < 10 larvae/dip) (F (1, 84) = 740.229, p<.001). Habitat type also significantly influenced larval density (F (2, 84) = 81.246, p<.001), with rain pools supporting the highest densities (M = 33.33 larvae/dip) and proving significantly more favourable than hoofprints and swamps (p<.001 for both comparisons). Physicochemical analysis revealed significant differences: preferred sites had higher mean temperatures (M = 33.77 °C, SD = 0.85 vs. M = 31.50 °C, SD = 0.96; t(4) = 3.053, p = .038), higher electrical conductivity (M = 1289.33 µS/cm, SD = 194.74 vs. M = 542.67 µS/cm, SD = 115.98; t(4) = 5.076, p = .005), higher total dissolved solids (M = 581.67 mg/L, SD = 82.78 vs. M = 273.33 mg/L, SD = 58.38; t(4) = 5.272, p = .006), and a lower pH (M = 7.10, SD = 0.15 vs. M = 8.03, SD = 0.40; t(4) = -3.837, p = .019) compared to non-preferred sites. Bacterial populations were isolated, and 16S rRNA gene sequencing revealed distinct profiles: Enterobacter species predominated in preferred sites, while Plualibacter species were more common in non-preferred sites. Bioassays demonstrated a significant preference for bacterial isolates from preferred sites (Mann-Whitney U = 0.000, p = .003). Specifically, Enterobacter sp. strain CDB3 (from a preferred site) elicited the highest mean number of eggs (M = 126.00, SD = 11.53) and an Oviposition Actrivity Index (OAI) of 0.84. Conversely, Pluralibacter gergoviae strain PGBM32 and an uncultured bacterium clone (both from non-preferred sites) attracted no eggs (OAI = -1.00). These findings highlight that specific physicochemical conditions and associated bacterial communities, particularly Enterobacter species, significantly attract An. arabiensis for oviposition, whereas others, like certain Pluralibacter species, may act as deterrents. This research underscores the potential for developing novel, microbe-based “push-pull” strategies for sustainable malaria vector control, to control mosquito breeding behaviours. This study suggests eco-friendly bactericides can reduce mosquito egg laying by removing attractant bacteria, aiding malaria vector control in malaria-prone areas.enThesis