Abstract: An eighteen amino acid neuropeptide isolated from brain complexes of adult female cockroach, Diploptera punctata, is identified as an allatostatin because it inhibits the biosynthesis of juvenile growth hormone in cockroach corpora allata. Primary structure of the isolated allatostatin is Al a-Tyr-Ser-Tyr-Val-Ser-Glu-Tyr-Lys-Arg-Leu-Pro-Val-Tyr-Asn-Phe-Gly-Leu-NH.s ub.2. A synthetic peptide of this sequence and three synthetic peptides with truncated sequences conserving the amidated carboxyl portion of the native sequence have allatostatin activity. Certain derivatives of the peptides also have allatostatin activity including compounds having the sequence: X-Val-Tyr-Asn-Phe-Gly-Leu-NH.sub.2, in which X is Leu-Arg, Leu-Pro, Arg-Leu-Pro-, Ala-Tyr-Ser-Tyr-Val-Ser-Glu-Tyr-Lys-Arg-Leu-Pro, acetyl-Ala-Tyr-Ser-Tyr-Val-Ser-Glu-Tyr-Lys-Arg-Leu-Pro, or acetyl-Arg-Leu-Pro. These peptides have the potential for regulating the growth of certain insects, and may be useful in the area of insect control.