Four million species of insects currently living on the earth are descendants of the common ancestor that emerged approximately 400 million years ago. The insect genomes, which contain about 20,000 genes respectively, have been evolving not only by maintaining the ancestral genes, but also by creating novel genes or losing old genes. The morphological and ecological diversity of the insects are expressed by diverse structures and functions of insect genomes among species/strains. I study to understand how the lepidopteran insects (moths and butterflies) realize the specific functions, by using silkworm, Bombyx mori as a model insect and genetics, molecular biology, biochemistry, and histology as methods. The current subjects of my rese arches are as follows; "Genetic network controlling sex determination in lepidopteran insects", "Characteristics of the Bombyx mori genome", "Genetic mechanism of the embryonic diapause in Bombyx mori", "Lateral gene transfers from Bacteria to Lepidoptera", and "Retrovirus-like elements in the Bombyx genome". These studies can contribute to basic biology as well as applied insect sciences including development of selective insecticides based on the genomic information and industrial utilization of insect- specific genes and molecules.