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Abstract-Activities of enzymes representative of glycolytic and p-oxidative pathways and citric acid and glycerophosphate cycles were measured in the developing flight muscles of three species: Calliphora erythrocephala, Locusta migrutoria, and Philosamia Cynthia. The activities were measured in vitro under optimal conditions. The enzyme pattern of young flight muscles is quite different from the adult pattern. In the second half of the developmental period final differentiation towards the adult metabolic pattern takes place, in Calliphora leading to exclusively carbohydrate-oxidizing capacities, in Locusta to properties enabling both aerobic glycolytic and P-oxidative processes, whereas Philosamiu becomes oriented to fatty acid oxidation. This differentiation starts after a temporary rise of lactate dehydrogenase activity, a phenomenon that seems to be connected with invagination of tracheoblasts into the muscle fibres. This tracheolization might be necessary for differentiation towards the species specific metabolic properties of the adult flight muscle.Theoretical aspects of the enzyme activities, as they were measured in the in vitro assays, are discussed and related to the physiological qualities of the flight muscles of the three species investigated.

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Abstract~Glycogen reserves in the fat body of Locusta migratoria decrease dramatically during the first two hours of flight. In fat body of rested locusts only 10~o of glycogen phosphorylase occurs in the active form. The enzyme is activated significantly during flight, when up to one-third of the total phosphorylase becomes active. Plaosphorylase activation can also be accomplished by injection of corpus cardiacum extracts, to give a maximum of circa 75~o active enzyme. Locust fat body is shown to contain protein kinase activity, which can be activated both by cyclic AMP and cyclic GMP. Apparent Ka-values are 0.13/~M for cyclic AMP and 0.16/~M for cyclic GMP. Results are discussed in relation to regulation of substrate utilization during flight.

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