Repellency and toxicity effects of selected plant essential oils against <em>Anopheles gambiae</em>

Plant-derived essential oils show significant potential as eco-friendly agents in controlling disease vectors, including mosquitoes and other arthropods. This study assessed the repellent properties and spatial toxicity of selected plant essential oils against the Anopheles gambiae Kisumu Susceptible Strain (KSS). Essential oils were extracted from Hyptis suaveolens (Bush mint), Ocimum gratissimum (Scent leaf), Nicotiana tabacum (tobacco), Ageratum conyzoides (goat weed), and Citrus sinensis (sweet orange) via steam distillation. The repellency and spatial toxicity against Anopheles gambiae KSS were evaluated using the WHO tube and Peet-Grady Chamber methods, respectively, using WHO guidelines, with N, N-diethyl-meta-toluamide (DEET, 10% w/v) and Deltamethrin (0.05% w/v) as controls. The data obtained were analysed using ANOVA with Tukey’s HSD and probit. Hyptis suaveolens and Ageratum conyzoides exhibited strong repellent effects 30 minutes after exposure, with effectiveness ranging from 96.5% to 100%, outperforming DEET, which showed 86.67% repellency. The tested plant essential oils demonstrated statistically significant repellent properties (p<0.05), ranging from 96% to 100% at concentrations of 0.3 and 0.5 mg/mL, outperforming DEET. Essential oils from C. sinensis, O. gratissimum, and N. tabacum showed 100% knockdown at a concentration of 0.5 mg/mL, demonstrating comparable efficacy with deltamethrin. At 0.3 mg/mL, O. gratissimum showed 100% mortality of Anopheles gambiae KSS within 60 minutes post-exposure, indicating strong knockdown potential. All oils at 0.3 and 0.5 mg/mL achieved 100% mortality after 24 hours post-exposure. Ocimum gratissimum at 0.5 mg/mL showed the most expedient knockdown times (KDT50 and KDT95). These results highlight the repellent and toxicity effects of the tested plant essential oils against An. gambiae KSS, suggesting their potential application as alternatives to synthetic insecticides for An. gambiae management strategies.