The greater wax moth Galleria mellonella L. (Lepidoptera: Pyralidae) is a model insect widely used for ecotoxicological studies and a serious pest of honeycomb in hives causing considerable losses in apiculture. Our aim was to explore the lethal and sublethal effects of juglone (5-hydroxy-1,4-naphthoquinone), a secondary metabolite naturally synthesised in leaves and fruits of the walnut species in the genus Juglans, on G. mellonella. According to probit analysis, the lethal (LC99) and median lethal (LC50) concentrations of dietary juglone given to G. mellonella larvae were determined as 5.49 and 2.38 mg / 2 g of diet, respectively. All tested juglone concentrations decreased the survivability of larvae to the pupal and subsequently to the adult stages. Selected juglone concentrations at LC30 (1.59 mg / 2 g), LC50 (2.38 mg / 2 g) and LC70 (3.18 mg / 2 g) incorporated into the diet of first instar larvae altered the life-history traits by prolonging the larval developmental time, decreasing pupal and adult weights, lowering total egg numbers and egg hatchability. Our results indicated that juglone has ecotoxic potential for insects and could be incorporated in novel studies on plant-based insecticides against storage insect pests.