7.1.3. Emulation and application of two-dimensional temperature fields

Thus, investigating the trajectories of bees in two-dimensional, complex and dynamic gradient fields is an important field of research to understand the navigation principles of single honey bees as well as the process of collective aggregation. In addition to investigating the locomotion of single and multiple bees in such two-dimensional temperature fields for the sake of fundamental research, such methods could also be used as simple bio-assays to measure some important fitness variables (e.g. based on social capabilities) of bees reared under different conditions (incubation temperature of brood, diet, insecticide exposure, genetic traits etc.).

Single bees or groups of honey bees can be studied in an arena as they move through a well-defined two-dimensional thermal gradient (Fig. 10) or form aggregations at optimal temperature spots (Fig. 11). A number of behavioural parameters such as moving speed or resting durations of individuals or aggregation time and cluster stability can be evaluated to quantify the locomotion behaviour of the bees and to determine their efficiency in finding an area of preferred temperature. This efficiency can be reduced by environmental factors that affect the thermotactic capabilities of the bees (e.g. chemicals or parasites). By comparing the behaviour between healthy and irritated individuals or between groups with different ratios of irritated to healthy individuals, the extent can be assessed to which different types of irritations compromise the bees at the level of individuals or at colony level.

Fig. 10. Two bees exhibiting different forms of locomotion behaviour. The trajectories of two bees moving in the arena for 20 min are shown along with their starting (triangle) and stopping positions (circle). A thermal gradient spans the arena, whose area of optimum temperature is designated by a red border. The bees exhibit different locomotion behaviours. While A performs a slightly biased random walk, B follows the arena wall most of the time.

1293PN revised Fig 10


Fig. 11. Timeline of an aggregation experiment. 128 bees move in a thermal gradient with the optimum spot (36 °C) at the left side and the coolest spot (32.5 °C) to the right. After being released at the centre of the arena (A) the bees quickly disperse across the arena (B). After 5 min, most of the bees are aggregated in a cluster at the optimal area (C), where they remain till the end of the experiment (D).

1293PN revised Fig 11