Fig. 4. Results of the critical tests in Series 3 experiments carried out at the Bee Station at Wuerzburg University. The visual patterns were black/white horizontal versus vertical gratings at the feeder and at the hive. However, the horizontal grating at the feeder and the vertical grating at the hive were the positive patterns in the morning, whereas the vertical grating at the feeder and the horizontal grating at the hive became the positive patterns in the afternoon. Results for one pattern are given. The results showed that trained bees significantly reverse their pattern preference (A) at the feeder and (B) at the hive entrance following midday breaks, as well as after an overnight break. The trained bees also had a significantly different pattern preference at the feeder and at the hive entrance within each testing period. The modulation of the average choice frequency, with reference to the horizontal grating could be approximated very well by a sinusoidal curve with a frequency of 0.52, i.e. a period of 12 h. The correlation coefficient was 0.97 for both the feeder and the hive. However, the phase of the sinusoidal curve at the hive was shifted 180° with reference to the feeder. See text for further details. Terminology for the test types: M, morning; A, afternoon; H, hive; F, feeder; 1, early; 2, late. ^***P<0.001.