Substrate usage and its regulation during flight and swimming in the backswimmer, Notonecta glauca

.  The metabolites that are generally used by insects during exercise are present in quite different concentrations in the haemolymph of the backswimmer Notonecta glauca L. Lipids are most abundant (between 10 and 20 mg/mL), whereas carbohydrates (2–3 mg/mL) and proline (approximately 1 mg/mL) are at very low concentrations. Injection of an extract of conspecific corpora cardiaca causes pronounced hyperlipaemia in the backswimmer. A neuropeptide with the same effect was isolated from the corpora cardiaca in a single high‐performance liquid chromatography (HPLC) step; the primary sequence was deduced from mass spectrometric measurements (matrix‐assisted laser desorption/ionization‐time of flight and electrospray quadrupol time‐of‐flight mass spectrometry) of whole corpora cardiaca, and the mass was confirmed in the HPLC fraction that had adipokinetic activity. The biologically active octapeptide has the sequence pGlu‐Val‐Asn‐Phe‐Ser‐Pro‐Ser‐Trp amide, which was characterized previously from the corpora cardiaca of the Emperor dragonfly, Anax imperator , and denoted Anaim‐adipokinetic hormone (AKH). The synthetic Anaim‐AKH peptide causes lipid mobilization when injected at a dose of 1 pmol into N. glauca . When other synthetic AKH members that occur in Hemiptera are injected into N. glauca at the same dose, the hyperlipaemic responses are significantly lower than after injection of Anaim‐AKH. Because only lipids increase upon activity, such as continuous swimming for 1 h or during a 1‐h rest period after a 3‐min flight episode in the laboratory, it is assumed that Anaim‐AKH serves as a true adipokinetic hormone in the backswimmer during bouts of natural swimming and flight.