Time-resolved repellency of botanical extracts against Anopheles gambiae and Anopheles funestus: A kinetic and chemical profiling approach

The rising demand for sustainable mosquito repellents has driven interest in bioactive plant extracts with prolonged efficacy. This study evaluated plant powders/ extracts from Striga hermonthica (S), Hyptis spicigera (H), and Lantana camara (L)—including their binary blends (LS, LH, and HS)—for repellency against wild Anopheles gambiae s.l. and Anopheles funestus mosquitoes using an olfactometer and hand-in-cage assays, respectively. A Repellency Index (RI) was used to assess repellency performance, supported by decay rate analysis, complete protection time (CPT), and a linear mixed-effects model incorporating time × sample interaction terms. LS and HS demonstrated increasing or stable repellency over time, supported by positive time × sample slopes (0.0065 and 0.0057, respectively) and positive, near-zero decay rates (+0.0024 and +0.0029, respectively). In contrast, LH and S alone, despite strong baseline RIs, showed faster decay (–0.0094 and –0.0091). Ethanol extracts consistently outperformed hexane counterparts, with higher CPT and efficiency values—LS (ethanol) achieving 178.7 minutes of CPT and efficiency of 243.1 minutes per unit RI. Compounds identified aligned with kinetic trends: quinonoids may have contributed to a strong initial repellency, while phthalate/ quinonoids likely acted as synergists, enhancing retention and stability. Notably, phytol may explain LS's extended efficacy. The integrated kinetic strategy—linking RI, decay rates, time × sample interactions, and efficiency to compound content—offers a cost-effective means to triage active and synergistic compounds within large GC–MS datasets. This chemobehavioral framework supports the development of optimized botanical repellent blends, reducing reliance on long-route compound-by-compound bioassays. • A time-resolved framework linked GC–MS data with repellency metrics (RI, CPT, decay rate) for plant-based samples. • Ethanol extracts outperformed hexane, with LS and HS blends showing extended protection (CPT: 178.7 and 91 min). • Positive decay rates (+0.0044, +0.0035) and high efficiency (243.1, 136.8 min/RI) confirmed sustained performance. • Blends containing phytol, phthalates, and quinonoids showed sustained or improving repellency over time. • The approach enables rapid screening of natural repellents without exhaustive compound-by-compound assays.