MODULATION OF NEGATIVE WORK OUTPUT FROM A STEERING MUSCLE OF THE BLOWFLY CALLIPHORA-VICINA

Of the 17 muscles responsible for flight control in flies, only the fi rst basalar muscle (b1) is known to fire an action potential each and every wing beat at a precise phase of the wing-beat period. The phase of action potentials in the b1 is shifted during turns, implicating th e b1 in the control of aerodynamic yaw torque. We used the work loop t echnique to quantify the effects of phase modulation on the mechanical output of the b1 of the blowfly Calliphora vicina. During cyclic leng th oscillations at 10 and 50 Hz, the magnitude of positive work output by the b1 was similar to that measured previously from other insect m uscles. However, when tested at wing-beat frequency (150 Hz), the net work performed in each cycle was negative. The twitch kinetics of the b1 suggest that negative work output reflects intrinsic specialization s of the b1 muscle. Our results suggest that, in addition to a possibl e role as a passive elastic element, the phase-sensitivity of its mech anical properties may endow the b1 with the capacity to modulate wing- beat kinematics during turning maneuvers.