A cDNA encoding a cathepsin D homologue was cloned from a cDNA library of the mulberry longicorn beetle, Apriona germari. Sequence analysis of the cDNA encoding the cathepsin D homologue of A. germari revealed that the 1,158 bp cDNA has an open reading frame of 386 amino acid residues. The deduced protein sequence of the A. germari cathepsin D homologue shows high homology with cathepsin D in insects, Aedes aegypti (68.2% amino acid similarity) and Drosophila melanogaster (67.2% amino acid similarity). Two aspartic residues and six cystein residues in the A. germari cathepsin D homologue are present at identical locations in all of the other catepsins D. Unlike cathepsins D in two insect species, A. gemari cathepsin D homologue appears to have two putative glycosylation sites, rather than one. Phylogenetic analysis revealed the A. germari cathepsin D homologue is more closely related to insect cathepsins D than to the other animal cathepsins D. Northern blot analysis suggests that A. germari cathepsin D homologue gene is expressed in most if not all, body tissues.