Effects of the chitin synthesis inhibitor diflubenzuron (DFB) on the integument of 5th instar Galleria mellonella L. larvae were investigated. When larvae were fed with semi-artificial diets containing 250, 500 and 1000 ppm of the compound, DFB affected the integument. The affected larvae failed to ecdysis, their cuticle was ruptured, lost haemolymph and blackened. In treated larvae, cuticle deposition was disrupted and the cuticle thickness was decreased by ∼50% compared with the untreated control, particularly at day 3 1/2. However, statistically there was no significant difference among the three concentrations (P>0.05). This may indicate that all three concentrations are equally effective in decreasing level. DFB at 500 and 1000 ppm also affected the epidermal cells and caused the occurrence of vacuoles.