Assessment of mosquito repellent efficacy of different formulations from tithonia diversifolia, cymbopogon citratus, and eucalyptus globulus

Abstract

Mosquito-borne diseases remain a major public health concern, particularly in sub-Saharan Africa. Growing limitations of synthetic repellents including resistance, environmental concerns, and safety issues have increased interest in plant-based alternatives. This study evaluated the repellent efficacy of essential oil formulations from T. diversifolia, C. citratus, and E. globulus against anopheles gambiae mosquitoes. Plant essential oils extracted via hydro-distillation, were characterized using FTIR and GC–MS for 1,8-cineole in E. globulus citral in C. citratus, and d-limonene in T. diversifolia. Individual essential oils were tested at 12% ,15% and 18%v/v test concentrations of the main active repellent compounds. Three Polyherbal blend formulations; Blend A (12%), Blend B (15%), and Blend C (18%) were prepared using the minimum effective concentrations of T. diversifolia (15%), C. citratus (12%), and E. globulus (12%). Repellency efficacy of the individual oils versus the blended formulations against Anopheles gambiae was assessed following the Surface Landing method with Odomos and methanol as the positive control and negative control respectively. At 12%, Blend A maintained 89.0 ± 2.0% repellency at 4 h and 15.0 ± 0.2% at 8 h, compared with 01EO (59.0 ± 1.4%, 1.0 ± 0.0%), 02EO (88.7 ± 1.6%, 11.0 ± 0.0%), and 03EO (83.1 ± 1.7%, 10.0 ± 1.5%), with significant differences for 01EO at all time points and with 02EO and 03EO at later hours (p < 0.05). At 15%, Blend B retained 82.4 ± 1.5% and 78.0 ± 2.0% repellency at 5–6 h and 20.2 ± 0.5% at 8 h, exceeding 01EO (86.6 ± 1.8%, 73.3 ± 0.0%, 10.0 ± 0.0%), 02EO (85.0 ± 1.6%, 72.8 ± 1.5%, 15.0 ± 1.7%), and 03EO with significant differences for all individual oils at later hours (p < 0.01-0.001). At 18%, Blend C maintained 96.4 ± 2.5%, 86.0 ± 1.0%, and 60.0 ± 0.5% repellency at 5, 6, and 8 h, respectively, compared with 01EO (68.0 ± 1.6%, 36.0 ± 1.6%, 10.0 ± 1.4%), 02EO (90.0 ± 0.0%, 83.3 ± 1.7%, 30.0 ± 0.0%), and 03EO (89.0 ± 1.7%, 80.2 ± 1.7%, 40.0 ± 1.9%), with Blend C significantly outperforming all oils at most time points (p < 0.05-0.001). Findings from this study indicate that blends are more effective than individual oils and show that potential synergistic blending significantly improves both potency and duration.