Biogenic peptide that prevents the onset of metamorphosis from larva to pupa. Has repressive activity against juvenile hormone esterase. Induces cell proliferation at low concentrations and inhibits it at high concentrations. Mediates the spreading of plasmatocytes to foreign surfaces. May have a role in the regulation of dopamine concentrations. Expressed in the hemolymph, perineural cells and neuroglia of larval brain. Levels are highest on day 0 of penultimate instar larvae and then decrease throughout larval growth with a temporary increase on day 0 of the last larval instar. In parasitized larvae, expression increases within one day of parasitization with elevated levels persisting for one day, declining gradually, rising and then declining again. By parasitization and low temperatures. Growth-blocking peptide appears to exist in two different forms, a long form which has been isolated from parasitized larvae and a short form which is found in non-parasitized larvae. The stop codon of the short form may be read as a Tyr to synthesize the long form. Belongs to the GBP/PSP1/paralytic peptide family.