CARBOHYDRATE AND FAT AS A FUEL FOR INSECT FLIGHT . A COMPARATIVE STUDY

From a metabolic point of view, three different types of insect flight muscles can be distinguished: muscles that degrade only carbohydrates, those depending only on fatty acids, and a third type in which both substrates can be oxidized. In the flight muscles examined no quantitative differences in the activities of the citric acid cycle enzymes were observed, although between the various insects during flight differences exist in respiratory rate. On the other hand, strict relations are present between respiration and the glycolytic or β-oxidative pathway in Apis, Locusta, and Actias. The activities of the two enzymes of the glycerophosphate cycle are directly correlated with the glycolytic capacity of the flight muscles. Fatty acid oxidation is supposed to be advantageous for migratory animals and insects that do not feed in the adult stage. Before the onset of migratory flights carbohydrate-metabolic processes in the flight muscles might be responsible for reaching optimal thoracic temperatures. © 1969.