Repellency and chemical composition of essential oils from four medicinal plants against Anopheles arabiensis (Diptera: Culicidae) under laboratory conditions.

Botanical repellents provide a traditional means of personal protection, yet optimizing their formulations is increasingly required to address shifting mosquito feeding behaviors and mitigate disease transmission. The current study aimed to evaluate the repellent efficacy of essential oils and their binary combinations as complex matrices against Anopheles arabiensis bites, the major malaria vector in Ethiopia. Essential oils were extracted from fresh parts of four ethnobotanically investigated medicinal plants in the Ghibe Valley, Ethiopia, namely Croton macrostachyus, Echinops kebericho, Eucalyptus globulus, and Juniperus procera using hydrodistillation. The chemical composition of the essential oils was analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). Arm-in-cage bioassays using laboratory-reared mosquitoes and human volunteers determined the effective dosage and complete protection time of the essential oils at 10% and 20% concentrations. A total of 131 chemical constituents were identified across the four analyzed essential oils. The C. macrostachyus leaf and seed oils provided a significantly longer protection time (p < 0.001), reaching 180 minutes with a mean percentage repellency of 85% to 100%. The essential oil of J. procera blended with C. macrostachyus or E. kebericho exhibited significant synergistic repellency (p < 0.001). The protection duration demonstrating by C. macrostachyus oil underscores their potential to meet the regulatory performance standards for natural insect repellents. Future investigations should include larger sample sizes, dermal toxicity assessments and field validation to fully support the commercialization of these essential oils.