Changes in energy reserves during flight of the desert locust, Schistocerca gregaria.

-1. Amounts of glycogen and glucose in locust haemolymph and fat body increase during the first 15 rain of flight but later fall to below the resting values. 2. Amounts of trehalose in haemolymph and glycogen in gut wall decline throughout flight. 3. Variations in the concentrations of free amino acids in haemolymph are reported. 4. The concentration of lipid in the haemolymph increases to about three times the resting level during the first hour of flight. Concurrently, the proportion of lipid oxidized increases to reach a plateau about 50 rain after the beginning of flight. 5. Mechanisms for the overall control of fuel utilization in the locust a r e discussed. INTRODUCTION LOCUSTS use both fat and carbohydrate as fuels for flight. During long-distance flight fat seems to be the main fuel (Krogh & Weis-Fogh, 1951 ; Weis-Fogh, 1952) but in addition carbohydrate is used, particularly during the early stages of flight (Weis-Fogh, 1952). A number of measurements of changes in energy reserves in locusts during flight have been made. Weis-Fogh (1952) showed that total fat and glycogen decreased during locust flight. Beenakkers (1965) found that the concentration of esterified fatty acid in the haemolymph of Locusta migratoria increased considerably during flight. This observation was confirmed and accounted for by an increase in the diglyceride fraction for Schistocerca gregaria (Mayer & Candy, 1967) and for Locusta (Tietz, 1967). Carbohydrate is probably supplied to the flight muscles in the form of trehalose and glucose which are the main blood sugars in the locust (Howden & Kilby, 1960). Thus the concentration of trehalose in locust haemolymph is known to fall almost to zero during extended flight (Weis-Fogh, 1964) and both glucose and trehalose can be used by flight muscle in vitro to provide energy for contraction (Candy, 1968). Bficher and Klingenberg (1958) found that the concentrations of trehalose, glucose and glycogen in locust flight muscle fell considerably during a 2-hr flight. Other possible fuels for flight include amino acids. Thus Kirsten et al. (1963) have shown that the proline concentration of locust thoracic muscle falls considerably during a 2-hr flight.