Cockroaches have long been used as insect models to investigate the actions of biologically active neuropeptides. Here, we describe the cloning and functional expression in Chinese hamster ovary cells of an adipokinetic hormone (AKH) G protein-coupled receptor from the cockroach Periplaneta americana. This receptor is only activated by various insect AKHs (we tested eight) and not by a library of 29 other insect or invertebrate neuropeptides and nine biogenic amines. Periplaneta has two intrinsic AKHs, Pea-AKH-1, and Pea-AKH-2. The Periplaneta AKH receptor is activated by low concentrations of both Pea-AKH-1 (EC50, 5 x 10(-9)M), and Pea-AKH-2 (EC50, 2 x 10(-9)M). Insects can be subdivided into two evolutionary lineages, holometabola (insects with a complete metamorphosis during development) and hemimetabola (incomplete metamorphosis). This paper describes the first AKH receptor from a hemimetabolous insect.