Three allatostatins have been isolated from the mosquito Aedes aegypti. These peptides have the following structures: Ser-Pro-Lys-Tyr-Asn-Phc-Gly-Leu-amide, Leu-Pro-His-Tyr-Asn-Phe-Gly-Leu-amide, and Arg-Val-Tyr-Asp-Phe-Gly-Leu-amide. A cDNA encoding these peptides was isolated from an abdominal ganglia cDNA library and sequenced. It was found to encode two additional allatostatins: Ala-Ser-Ala-Tyr-Arg-Tyr-His-Phe-Gly-Leu-amide and Leu-Pro-Asn-Arg-Tyr-Asn-Phe-Gly-Leu-amide. Northern analysis of whole mosquito mRNA revealed a single prepro-allatostatin message of around 3,000 bases. Identification of a partial prepro-allatostatin cDNA from a midgut cDNA library shows that the same gene is also expressed in the mosquito midgut.