none Last instar larvae of the insect armyworm, Pseudaletia separata , parasitized with the parasitoid wasp, Apanteles kariyai , do not initiate metamorphosis and, ultimately, the wasp larvae emerge from the host larvae about 10 days after parasitization. It is necessary for the parasitoid wasp to perturb the armyworm's endocrinological processes that control normal metamorphosis from larvae to pupae. This endocrinological perturbation allows the parasitoid to complete its larval growth before emerging from the host larvae. A growth-blocking peptide with repressive activity against juvenile hormone esterase has been proven to exist in the parasitized host larval plasmas. Here, I describe the detailed structure of this peptide and also the corresponding synthetic peptide to confirm this structure. Biochemistry; Life cycle and development; Development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Pseudaletia separata (Noctuidae); Proteins; Larval development; Growth; Growth blocking peptide from hymenopteran parasite, structure; Hymenopteran parasites; Apanteles kariyai; Host growth blocking peptide, structural characterization Apanteles kariyai (Braconidae); Proteins; Lepidopteran host growth blocking peptide; Lepidopteran hosts; Pseudaletia separata; Host growth blocking peptide, structural characterization