Abstract

Background: Larval habitat management is increasingly recognized as a complementary strategy for malaria vector control. While bacterial communities are abundant in mosquito breeding sites, their role in shaping oviposition behavior of Anopheles gambiae (Diptera: Culicidae) remains poorly understood. This study evaluated the relative attractiveness or repellency of water infused with bacterial isolates obtained from mosquito larval habitats to gravid Anopheles gambiae. Methods: We isolated and taxonomically characterized bacteria from 30 larval habitats in coastal Kenya using 16S rRNA sequencing. Thirty-two representative isolates were tested in two-choice oviposition bioassays with gravid An. gambiae s.s., and volatile organic compounds (VOCs) emitted were analyzed by GC-MS. Statistical analyses included Students t-tests, Mann-Whitney U tests, and calculation of the Oviposition Activity Index (OAI). Results Proteobacteria dominated larval habitats (78%), with frequent genera including Aeromonas, Acinetobacter, Pseudomonas, Enterobacter, and Cronobacter. Most isolates exerted strong deterrent effects, with Aeromonas hydrophila, Enterobacter hormaechei, and Pseudomonas mendocina completely inhibiting oviposition (OAI = -1; 100% repellency). Other isolates such as Neobacillus drentensis and Aeromonas veronii reduced egg deposition by >85%. In contrast, a small subset (Aquitalea pelogenes, Pseudomonas oleovorans, Cronobacter sakazakii) showed weak, non-significant attraction (OAI = 0.15-0.23). GC-MS revealed that highly repellent isolates emitted abundant benzenoids, ketones, phenols, ethers, oxygenated heterocycles, and aldehydes. Conclusions Bacterial volatiles strongly modulate oviposition site selection in An. gambiae, with most isolates acting as potent repellents. These findings highlight microbial VOCs as promising candidates for novel vector control strategies targeting gravid mosquitoes. Limitations include the laboratory-based bioassay design and lack of field validation of VOC activity. Future work should identify specific bioactive compounds and evaluate their efficacy under natural conditions.