At present the honeybee is one of the very few invertebrates in which sleep-like behavior, similar in many respects to mammalian sleep, is known to exist [1, 2]. We now describe a new video interface which allows behavioral investigations of the microstructure of sleep in honeybees. The method permits contactless measurements of position and motion of parts of the body and the appendages with high accuracy and high temporal resolution (max. 50 measurements per s).

The video interface was developed in collaboration with the Department of Electrical Engineering and Information Technology of our university¹. The device scans contours by insertion of 4 measuring lines (2 horizontal and 2 vertical lines) into a video image. Starting at a certain point of the video image, the measuring line stops at a point which has a previously defined contrast with the background. The positions of the measuring lines on the video image as well as their starting points and the contrast thresholds of the contours can be chosen freely. During each half-frame, the lengths of the 4 measuring lines are determined. The measured values are available in analog (voltage) as well as in digital form at the corresponding output. It is possible to transfer either the coordinates of the starting points of the measuring lines or the measured values (lengths of the measuring lines; for each measuring line the range is between 0 and 255 pixels) to a computer. For both the display of the coordinates and the data logging we have developed suitable software. The video interface can be used during an experiment (on-line operation) as well as for later evaluation of video tapes (off-line operation).

For data processing and the subsequent time-series analysis with appropriate mathematical procedures we have developed a whole software package which allows treatment of the raw data in manifold ways. For example, one of these programs categorizes antennal motility, whereas another program determines the start and finish of ventilatory episodes. The video interface has already been used successfully for the analysis of a large number of video tapes. These video tapes were obtained during investigations of the nightly behavior of honeybees [3, 4, 5, 6].

¹ Our thanks to Prof . W. Zschunke and his team.

References

1. Kaiser, W.; Steiner-Kaiser, J. (1983). Neuronal correlates of sleep, wakefulness and arousal in a diurnal insect. Nature, 301, 707-709.
2. Kaiser, W. (1988). Busy bees need rest, too - behavioural and electromyographical sleep signs in honey bees. J. Comp. Physiol. A, 163, 565-584.
3. Sauer, S.; Kaiser, W.; Sauer, M. (1997). The microstructure of sleep in honey bees - a statistical analysis of antennal immobility. Verh. Dtsch. Zool. Ges., 90.1, 316.
4. Sauer, S.; Kinkelin, M.; Kaiser, W. (1997). Sleep in honey bees is a dynamic process. Apidologie, 28, 213-215.
5. Sauer, S.; Herrmann, E.; Kaiser, W. (1998). The temporal occurrence of antennal motility during sleep in honey bees can be described by a non-stationary Poisson process. Proc. 26th Göttingen Neurobiol. Conf., Vol. II, 266, Thieme-Verlag.
6. Sauer, S.; Kaiser, W. (1998). Another dynamic sleep sign in honey bees: discontinuous respiration. Zoology, 101 (Suppl. I), 67.