The utilization of reserve substances in Drosophila during flight

The respiratory quotient in Drosophila during flight is about 1·0 (Chadwick, 1947), and the duration of flight to exhaustion varies with the age of the fly in the same manner as does the total glycogen—increasing steeply during the first 5 days of adult life, remaining at a maximum for about 10 days and then falling gradually until the fly is 5 or 6 weeks old (Williams, Barness & Sawyer, 1943). It appears certain that glycogen is the main or sole reserve substance consumed during flight. It is the object of the present work to provide a histological picture of the distribution of the reserve substances and their mobilization during sustained flight. In the course of the work it has been possible to compare directly the efficiency of different substances as sources of energy for flight. D. melanogaster has been used throughout. The insects have been reared and maintained on standard maize-meal medium at 250C.