Mechanisms of black and white stripe pattern formation in the cuticles of insect larvae

Molecular mechanisms that produce pigment patterns in the insect cuticle were studied. Larvae of the armyworm Pseudaletia separata have stripe patterns that run longitudinally along the body axis. The pattern in the cuticle became clear by being emphasized by the increasing contrast between the black and white colors of the lines after the last larval molt. We demonstrated that dopa decarboxylase (DDC) mRNA as well as protein are expressed specifically in the epidermal cells under the black stripes. The pigmentation on the stripes was clearly diminished by injection of a DDC inhibitor (m-hydroxybenzylhydrazine) to penultimate instar larvae for 1 day before molting, suggesting that DDC contributes to the production of melanin. Further, electron microscopic observation showed that the epidermal cells under the gap cuticle region (white stripe) between the black stripes contain many uric acid granules, which gives a white color. Our findings suggest that the spatially regulated expression of DDC in the epidermal cells produces the black stripes while abundant granules of uric acid in the cells generate the white stripes in the cuticle. Based on these results, we concluded that this heterogeneity in the epidermal cells forms cuticular stripe patterns in the armyworm larvae.