A FREE-RUNNING BIMODAL CIRCADIAN-RHYTHM IN THE TSETSE-FLY GLOSSINA-LONGIPENNIS

In nature, the tsetse fly, Glossina longipennis Corti, restricts its a ctivity to similar to 1h around sunset and a lesser peak at dawn. This markedly crepuscular rhythm was investigated in actographs under cons tant conditions in the laboratory. In LD 12:12 with 30-min dawns and d usks, the evening activity started as the lights dimmed, peaked in the first hour of darkness, and then declined rapidly to near zero, to pe ak again for similar to 1h at dawn. Virtually no activity occurred thr ough the central 8 light hours of the photophase. In constant darkness , this pattern of a major 'dusk' and minor 'dawn' peak was repeated in the males for at least three cycles, with a free-running period of si milar to 23h. This is the first demonstration of a fully endogenous bi -modal rhythm is testse flies.