THE CONTROL OF WING KINEMATICS AND FLIGHT FORCES IN FRUIT-FLIES (DROSOPHILA SPP.)

By simultaneously measuring flight forces and stroke kinematics in sev eral species of fruit flies in the genus Drosophila, we have investiga ted the relationship between wing motion and aerodynamic force product ion, We induced tethered flies to vary their production of total fligh t force by presenting them with a vertically oscillating visual backgr ound within a closed-loop flight arena, In response to the visual moti on, flies modulated their flight force by changing the translational v elocity of their wings, which they accomplished via changes in both st roke amplitude and stroke frequency, Changes in wing velocity could no t, however, account for all the modulation in flight force, indicating that the mean force coefficient of the wings also increases with incr easing force production, The mean force coefficients were always great er than those expected under steady-state conditions under a variety o f assumptions, verifying that force production in Drosophila spp, must involve non-steady-state mechanisms, The subtle changes in kinematics and force production within individual flight sequences demonstrate t hat flies possess a flexible control system for flight maneuvers in wh ich they can independently control the stroke amplitude, stroke freque ncy and force coefficient of their wings, By studying four different-s ized species, we examined the effects of absolute body size on the pro duction and control of aerodynamic forces, With decreasing body size, the mean angular wing velocity that is required to support the body we ight increases, This change is due almost entirely to an increase in s troke frequency, whereas mean stroke amplitude was similar in all four species, Despite the elevated stroke frequency and angular wing veloc ity, the translational velocity of the wings in small flies decreases with the reduction in absolute wing length, To compensate for their sm all size, D. nikananu must use higher mean force coefficients than the ir larger relatives.