Larvicidal Potential of Cola nitida Endophytic Bacteria Against Insecticide-Resistant Anopheles gambiae
Background Innovative vector control strategies are urgently needed to combat malaria transmission by Anopheles gambiae, given the limitations of current insecticides—namely resistance, human toxicity, environmental damage, and high costs. This study evaluated the larvicidal efficacy of endophytic bacteria isolated from Cola nitida against third-instar larvae of Anopheles gambiae. Methods Endophytic bacteria were isolated from nine Cola nitida plant parts (leaves, roots, stems, fruits, flowers, stem bark, branches, root bark, whole plant extracts) using standard surface sterilization and culturing protocols. Thirty-two morphologically distinct strains were purified and screened for larvicidal activity against third-instar An. gambiae larvae using the WHO-recommended turbidity method at McFarland 4 standard. Six active isolates underwent dose-response testing (McFarland 0.5-4) with mortality recorded at 24 and 48 hours. Environmental safety was assessed via Lemna minor growth inhibition, and molecular identification employed the API 20E biochemical gallery. Results Screening identified six strains with significant larvicidal activity (LC₅₀ < McFarland 2). At McFarland 2 concentration, all six strains achieved >50% mortality within 24-48 hours, with Lemna minor EC₅₀ >100% indicating minimal phytotoxicity. API 20E identification (96-99.99% similarity) revealed three strains (6164, 6211, 6501) matching Photobacterium damselae, two (6186-1, 6512-1) matching Salmonella enterica subsp. arizonae, and one (6600) matching Pseudomonas sp., confirmed by distinctive biochemical profiles. Conclusion This study provides the first evidence of potent, environmentally safe larvicidal activity from Cola nitida endophytic bacteria against Anopheles gambiae. These strains represent promising biocontrol candidates to address insecticide resistance, offering a sustainable alternative for malaria vector management in endemic regions.