The regulation of distance to dummy flowers during hovering flight in the hawk moth Macroglossum stellatarum

Abstract

1. While collecting nectar in hovering flight the European hawk moth Macroglossum stellatarum efficiently regulates its distance relative to flowers that are shaken by wind. This can be demonstrated in laboratory experiments by moving dummy flowers (blue cardboard disks) towards and away from the feeding animal ( Fig. 1).2. Distance regulation is predominantly mediated by visual cues. Mechanoreceptors on the proboscis appear to contribute little to the response.3. Movements of dummy flowers can be simulated by expanding and contracting a pattern projected onto a screen. With this technique we investigated the dynamical properties of the servo mechanism underlying distance regulation. The system behaves as a bandpass filter with corner frequencies of 0.15 and 5 Hz (Figs.2,3).4. When a high-speed ramp-like movement of the flower is simulated, there is an asymmetry in the response. During simulated approach the reaction is phasic-tonic with a pronounced overshoot at the beginning, during simulated retraction it remains tonic (Fig.5B,C).5. During distance regulation the animals compensate for the speed of the edge of the projected pattern. Distance regulation improves substantially when the number of stimulated elementary movement detectors is increased through increasing the number of contour lines by projecting concentric rings instead of a homogeneous disk (Figs.7, 8).

Visual position stabilization in the hummingbird hawk moth, Macroglossum stellatarum L. II. Electrophysiological analysis of neurons sensitive to wide-field image motion

“…The analysis of the optomotor behaviour in Macroglossum (Pfa and Varju 1991;Kern 1994;Farina et al 1994Farina et al , 1995Kern and Varju 1998) has been con®ned so far to position stabilization in the horizontal plane by compensatory translational and rotational movements. Hence, it is not possible to discuss the functional role of TV-and RVcells in an experimentally well-established framework.…”

“…Unfortunately, this response could not be analysed systematically owing to methodological limitations. Note that in free¯ight Macroglossum responds to an approaching, respectively, retreating dummy¯ower (diameter 2 cm) by moving back-andforth (Pfa and Varju 1991;Farina et al 1994).…”

“…Their age ranged between 2 days and 3 weeks. The animals were taken from the stock of the institute (for breeding and keeping of animals see Farina et al 1994;Kern 1994). They were demobilized by cold (5 min at 4°C) and, after removal of the legs, slid into a narrow plastic tube so that the wings were immobilized but the head and the prothorax were still accessible.…”

“…This peculiar feeding behaviour, which is reminiscent of hummingbirds, requires the ability of the animal to compensate for disturbances of its position relative to the¯ower in order to keep the proboscis in contact with the nectary. It has been shown in laboratory studies on freely¯ying animals that they control their position mainly by exploiting visual cues (Pfa and Varju 1991;Farina et al 1994Farina et al , 1995Kern and Varju 1998). Mechanical cues derived via the proboscis were demonstrated to play only a minor role (Zhou 1991).…”

Neuronal Encoding of Visual Motion in Real-Time

“…One such example is optomotor position stabilization of the hummingbird hawkmoth which hovers almost stationarily in front of flowers while sucking nectar. Flowers, on which the hawkmoth is feeding, were found to wiggle in the wind at frequencies between about 1 and 2 Hz and thus change their direction of motion on a relatively slow timescale (Farina et al 1994). Another example are the retinal image displacements experienced by solitary wasps while acquiring a visual representation of the environment of their nest in systematic orienting flights.…”