INSECT FLIGHT METABOLISM

Small amounts of substances are located in the flight muscles themselves to power the initiation of flight, but the initial store of ATP in muscle cells is only sufficient for a few

seconds of flight. The transfer of a phosphate group to ADP from arginine phosphate, providing an additional brief period of flight, replenishes it. The muscle may also store small amounts of other fuels including proline, glycogen, and triacylglycerol that are drawn upon during flight.

Flight muscles draw the next most immediate source of energy from substrates in the hemolymph. The disaccharide trehalose is present in high concentrations as a circulating energy source that is used during the early phases of flight.

Hemolymph diacylglycerol also bathes muscle cells, and the amino acid proline is utilized in some insects for flight.

These are mobilized from fat body reserves to maintain their levels in the hemolymph. The fuel for longer flights is stored in the fat body and transported to flight muscles through the hemolymph. This fuel use varies among insect orders.

Flight muscles completely oxidize carbohydrates to carbon dioxide and water

in the absence of any anaerobic metabolism. Glycolysis in insect flight muscle occurs much like that in other animals, with a few additions.

In general, insects that engage in long-range flights oxidize lipid, whereas those that use carbohydrate fly for only short periods. Insects with high wing-beat frequencies and asynchronous muscles tend to utilize carbohydrates, whereas those with synchronous flight muscles are more likely to utilize lipid. Lipid is the most concentrated form of energy storage.