The insecticidal activity of the essential oils peppermint, Mentha piperita L., geranium ; Pelargonium graveolens L., basil ; and Ocimum basilicum L. were investigated in laboratory against early fourth instar larvae of the greater wax moth, Galleria mellonella. The tested plant oils prolonged the larval - pupal periods and reduced both pupation and percentage of adult emergence. O. basilicum scored the highest larval mortality followed by M. piperita then P. graveolens. Other developmental aspects as survival and sex ratio were clearly affected by increasing the concentration increments of plant oils. The combined treatment of 100 Gy Gamma radiation and LC50 of M. piperita and P. graveolens had clear effect on total larval mortality and sex ratio. Pupation, adult emergence, and survival were clearly reduced in the combined treatments.