Menotaxis

Abstract

We have mentioned already on several occasions that Drosophila can maintain an arbitrary angular position relative to a visual object (e.g., a vertical stripe). If one tries to translate menotaxis at the torque compensator into the free flight situation, one is reminded of hoverflies hovering at a fixed position and orientation in mid-air. Hover flight of Drosophila is less perfect, but it too is characterized by stable orientations changed only by means of body saccades. Might the “quiet” flight mode (Fig. 53 c) at the torque compensator correspond to hovering flight? The absence of visual cues relating to forward motion, the lack of motion parallax and the low streaming velocity of the air (Fig. 26) most probably inform the fly about its “slow” forward speed. In fact, the discovery of Götz (1983) that differently oriented sets of EMD’s are mediating lift/thrust control, depending on whether the fly is flying in an air current or in still air, argues in favor of this conjecture. However, the fly’s horizontal body posture does not conform to hovering flight and gravity as well as the horizontal rotatory motion of the panorama keep the fly informed about its real orientation. Thus the fly at the torque compensator may be in a conflict as to its appropriate flight behavior (see similar argument on p. 46 f and 107f).

The term “menotaxis” will be used here for a behavioral mode in which the fly keeps the stripe at any angular position including the front (voluntary fixation; see Chap. 7)