<p>Our previous study demonstrated that blue light irradiation is lethal to various insect species and increases the generations of hydrogen peroxide (H₂O₂), a major reactive oxygen species (ROS), in <i>Drosophila melanogaster</i> Meigen (Diptera: Drosophilidae) pupae. We hypothesized that blue light penetrates the compound eyes and/or integument of the insect, is absorbed by chromophores or photosensitizers, generates ROS, damages tissues, and ultimately leads to death. To test the hypothesis, the role of compound eyes and the integument as blue light-input pathways were investigated using <i>D. melanogaster</i> adults with different phenotypes, including two wild types and seven mutants (<i>white</i>: white eyes, <i>sepia</i>: sepia eyes, <i>Bar</i>: bar eyes, <i>eye missing</i>: absence of eyes, <i>Cry</i>^<i>b</i>: loss of cryptochrome function, <i>norpA</i>: defect in phototransduction, <i>ebony</i>: melanic integument). The results revealed that <i>ebony</i> fly mortality was notably lower than that of the wild types, whereas other mutant strains showed similar or higher mortality rates compared to wild types. This suggests that blue light penetration through the integument plays a crucial role in toxicity, whereas compound eyes and cryptochromes are less critical blue light-input pathways. Furthermore, a positive correlation was observed between blue light transmittance through the abdominal integument and mortality, although the integument exhibited no specific wavelength selectivity. H₂O₂ levels were higher in flies irradiated with blue light compared to in non-irradiated flies, excluding <i>ebony</i>, among the three phenotypes tested (wild type, <i>white</i>, and <i>ebony</i>). The findings suggest that internal damage caused by blue light transmitted through the integument leads to death.</p>