A natural insecticide developed from the mixture of the essential oils (EOs) of Cymbopogon citratus (DC.) Stapf (Poaceae), Cedrus atlantica (Endl.) Manetti ex Carriére (Pinaceae), and Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson (Myrtaceae) was studied. The mixture of oils caused high mortality (LD50 = 0.018 μl/insect) to the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), a globally important pest, after topical application on adults. Based on the chemical characterization of biopesticide using gas chromatography-mass spectrometry (GC-MS) analysis, many of the constituents had known insecticidal properties (the monoterpenes α-citronellal and E-citral and the sesquiterpernes α-himachalene and β-himachalene, all at concentrations above 15%). Phytotoxicity tests on orange trees demonstrated that this natural product was harmless when the mixture was applied diluted in water with a surfactant. The mixture of EOs was also harmless (1, IOBC category) to the biological control agent responsible for reducing populations of tephritids, the parasitoid Psyttalia concolor (Hymenoptera: Braconidae), following exposure to treated orange trees in a semifield assay within a greenhouse, but killed 46.2% of C. capitata (Szépligeti) adults after 72 h. Our results suggest that mixture of EOs has potential for use as an adulticide against medfly, although the production price was exceedingly high compared with that of commercial synthetic insecticides. Therefore, we discuss the advantages and disadvantages related to the potential use of this natural insecticide.