Coleoptera, Oryctes monoceros, African Rhinoceros Beetle, Aggregation Pheromone, Ethyl 4-M ethyloctanoate Ethyl 4-m ethyloctanoate is a male-produced aggregation pheromone of the African rhinoceros beetle, Oryctes monoceros (Olivier). It was identified by coupled gas chromatographic-electroantennographic detection (GC -EAD) and coupled GC-mass spectrometry (MS) of Porapak Q-trapped male-produced volatiles. Natural and synthetic ethyl 4-m ethyloctanoate elicited comparable antennal responses. In a field experiment (La Me Research Station, Côte d’Ivoire), synthetic ethyl 4-methyloctanoate released at 30 mg/day attracted both male and fem ale Oryctes, whereas the known, non-beetle-produced attractant, ethyl chrysanthemate, did not attract any Oryctes. Upon improvement of trap design and placement, and the identification of synergistic (plant) volatiles, pheromone-based mass trapping may become an alternative and/or additional strategy to manage O. monoceros, one of the most destructive pests of commercial coconut, oil, and date palms in Africa.