Antibiotics are routinely incorporated in insect culture media. Although culturing insects on diets containing antibiotics is a decades-old practice, the antibiotics can exert deleterious effects on the insects. Diets amended with penicillin, streptomycin, fluconazole or griseofulvin were evaluated as to their impact on survivorship, development, wet weight, and adult total protein content of Galleria mellonella (L.). Insects were reared from neonates to adults on artificial diets containing 0.001, 0.01, 0.1 or 1.0 g of the antibiotics (per 100 g diet). Dose- and stage-dependent variations in both biological and biochemical parameters occurred. Penicillin at high concentrations significantly increased the wet weight of the insect, whereas low dietary fluconazole, griseofulvin and streptomycin concentrations significantly increased wet weight and high concentrations decreased wet weight. Dietary antibiotic treatment resulted in significantly decreased survivorship and increased developmental time of larvae. The diet amended with 1.0 g of either penicillin or streptomycin decreased pupation and adult emergence by 50%. Larvae reared on the diets supplemented with the highest concentrations of fluconazole and griseofulvin produced as low as 20% of adults. The 0.1 g fluconazole treatment prolonged adult development by 8 d. High dietary griseofulvin concentrations markedly decreased total protein content of adults. Other antibiotics also resulted in decreased total protein content in adults depending on their types and concentrations. Slightly enhanced survivorship, shortened development and increased total protein content were observed with some sublethal doses of antibiotics. It appears that dietary antibiotic impact on insect biological parameters is exerted via their deteriorative effects on biochemical factors in relation to alterations in wet weight. Low concentrations of these antibiotics can be used in artificial rearing of G. mellonella.