Juglone is a secondary metabolite naturally synthesized in leaves and green husks of the walnut plant species. It is an important phytochemical compound which has an insecticidal potential on the model insect Galleria mellonella (greater wax moth). Here, we aimed to investigate oxidative and genotoxic stress changes induced by juglone in G. mellonella larvae. In all assays, lethal concentrations (LC10: 0.5 mg; LC30: 1.5 mg; LC50: 2.3 mg) of juglone were directly incorporated into the 2 g diet of the first instar larvae of G. mellonella. Tissue homogenates of the last instars exposed to juglone were used to test for antioxidant enzyme activities (glutathione-S transferase, glutathione peroxidases, catalase, and superoxide dismutase) and the amount of malondialdehyde (MDA). Comet and Micronucleus assays were used to determine the genotoxic effects of juglone on the larvae. Juglone expressed changes in antioxidant enzyme activities and induced lipid peroxidation in a concentration-dependent manner. Significant DNA and chromosome damage occurred in the genome of the insect hemocytes. Increase in MDA levels and DNA damage indicate that juglone-dependent oxidative stress occurred in the larval body. Hence, juglone has concentration-dependent ecotoxic and genotoxic effects on the storage pest and model organism, G. mellonella.