Synergistic enhancement of natural mosquito repellents through matrix interactions: Insights from GC-MS and bioassays Luther K. Adjei a,* , Samson A. Abagale a , Kwame Anokye b a Department of Applied Chemistry and Biochemistry, C. K. Tedam University of Technology and Applied Science, Navrongo, Ghana b Department of Environmental Science, C. K. Tedam University of Technology and Applied Science, Navrongo, Ghana A R T I C L E INFO Keywords: Repellent compounds Olfactory Mosquito repellency Synergy ABSTRACT While plant-based mosquito repellents are considered safer alternatives to synthetic chemicals, their short-lived efficacy often diminishes their effectiveness. This study investigates a synergistic approach using a matrix of plant-derived samples to address this limitation and enhance their repellency. In olfactory studies, powdered samples and extracts—both individual and blended—were tested against Anopheles gambiae s.l. and Anopheles funestus in laboratory and semi-field environments. Euclidean distances, Hierarchical clustering, and heatmap analyses assessed compound relationships to repellent compounds that were literature-cited. Molecular finger- prints from SMILES identifiers and Tanimoto coefficients quantified structural similarity. Sample matrices significantly enhanced repellency, demonstrating superior performance in olfactory assays (e.g., Striga her- monthica vs. Lantana camara/S. hermonthica blend: W = 787, p = 0.0013) and extending protection times in human trials (179 vs. 67 minutes, t = 21.872, p < 0.001). GC-MS analysis revealed major compounds for S. hermonthica (Methyl-6-O-[1-methylpropyl]-α-galactopyranoside, 51.047 %), Hyptis spicigera (Cyclo- propanecarboxylic acid derivative, 87.137 %), and L. camara (1-Heptatriacotanol, 10.099 %). Phytol and a Phthalic acid derivative were identified, with monoterpenes ( )-Spathulenol and Cis-Z-α-Bisabolene epoxide possibly contributing to synergy. Heatmap and Tanimoto coefficient analyses revealed moderate structural similarities among compounds in active and inactive portions of sample matrices. Key compounds like Phytol and Phthalic acid derivatives, alongside potential synergists such as spathulenol and bisabolene, are hypothe- sized to contribute to the observed repellency. Long-chain primary alcohol 1-heptatriacotanol holds promise for optimizing plant-based repellents with extended and robust action. 1. Introduction Despite significant progress in reducing malaria-related mortality (Kleinschmidt et al., 2018), the persistent disease burden highlights the need for innovative vector control strategies. Current interventions, such as insecticide-treated nets (ITNs) and indoor residual spraying, are increasingly compromised by the emergence of insecticide-resistant mosquito populations. Vector resistance, particularly to widely used pyrethroids, has reduced the efficacy of these interventions, necessi- tating alternative solutions (Lengeler, 2004; Hamel et al., 2011; Tok- ponnon et al., 2019; Badmos et al., 2021; Chala and Hamde, 2021; Nyasvisvo. et al., 2024). Certain alternatives, such as deltamethrin and alphacyperthrin, have been effective, but concerns remain about the potential development of resistance (National Malaria Control, 2013). While plant-derived mosquito repellents offer a more sustainable alternative, their full potential remains underexplored and warrants deeper investigation. Beyond being environmentally sustainable and cost-effective, they are also a safer alternative to synthetic chemicals, which pose toxicity risks to humans and non-target species (Abbas et al., 2023; Sanei-Dehkordi et al., 2021). By addressing the limitations of current interventions, plant-based repellents could play a critical role in integrated vector management strategies (Effiom et al., 2012). 1.1. Selected mosquito-repellent plants S. hermonthica, also known as purple witchweed, is a parasitic flowering plant. In Africa, this parasitic weed, characterized by slender stems and purple flowers, poses a significant threat to cereal crops. H. spicigera, also known as spicate hyptis or Brazilian mint, is an her- baceous perennial plant belonging to the Lamiaceae family. Though * Corresponding author. E-mail addresses: lutheradjei@gmail.com (L.K. Adjei), samnabgh@yahoo.com (S.A. Abagale), anokyekwame73@gmail.com (K. Anokye). Contents lists available at ScienceDirect Biochemical Systematics and Ecology journal homepage: www.elsevier.com/locate/biochemsyseco https://doi.org/10.1016/j.bse.2025.105003 Received 2 December 2024; Received in revised form 10 March 2025; Accepted 11 March 2025 Biochemical Systematics and Ecology 121 (2025) 105003 Available online 20 March 2025 0305-1978/© 2025 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.