The halteres of the blowfly Calliphora

Abstract

We quantitatively analysed compensatory head reactions of flies to imposed body rotations in yaw, pitch and roll and characterized the haltere as a sense organ for maintaining equilibrium. During constant velocity rotation, the head first moves to compensate retinal slip and then attains a plateau excursion (Fig. 3). Below 500 ° /s, initial head velocity as well as final excursion de- pend linearily on stimulus velocities for all three axes. Head saccades occur rarely and are synchronous to wing beat saccades (Fig. 5). They are interpreted as spontane- ous actions superposed to the compensatory reaction and are thus not resetting movements like the fast phase ol `vestibulo-ocular' nystagmus in vertebrates. In addition to subjecting the flies to actual body rotations we developed a method to mimick rotational stimuli by subjecting the body of a flying fly to vibrations (1 to 200 µm, 13C to 150 Hz), which were coupled on line to the fly's haltere beat. The reactions to simulated Coriolis forces, mimicking a rotation with constant velocity, are qualita- tively and to a large extent also quantitatively identical tc the reactions to real rotations (Figs. 3, 7-9). Response, to roll- and pitch stimuli are co-axial. During yaw stimu- lation (halteres and visual) the head performs both a yam and a roll reaction (Fig. 3e,f), thus reacting not co-axial This is not due to mechanical constraints of the neck ar- ticulation, but rather it is interpreted as anadvance com- pensation' of a banked body position during free flight yaw turns (Fig. 10).