7.6. Advantages and disadvantages of the method
With this setup the researcher can observe the behaviour of individual honey bees or of groups with respect to their temperature optimum. The setup allows automated and reproducible experiments with dynamically changing thermal gradients. Examples of the questions which can be investigated with the described hardware are:
- The natural temperature preferendum and thermotactic behaviour of honey bees.
- The responses of individuals and groups to temperature changes on a local level.
- The influence of environmental factors (incubation temperature, diet, parasites, pesticides etc.) on individual and social (thermotactic) behaviour.
- The learning abilities of honey bees regarding circadian temperature
In light of the increasing environmental stress honey bee colonies have to deal with it is especially important to have a method available for the standardized investigation of the bees’ natural (healthy) behaviour and its modulation by compromising environmental factors. The bee arena facilitates such investigations with a focus on thermotactic behaviour, both on the individual level (temperature preferendum, locomotion and search behaviour) and on the collective level (aggregation behaviour, social interactions).
The advantages of the setup are:
- The very low price of the setup: the total price for the setup is approximately 10% of the price for a commercial thermovision camera.
- Due to the "do it yourself" nature of the setup it is easy to adapt it to new tasks (e.g. new bioassay).
- The given setup allows the researcher to easily replace the given sensors (temperature sensors in the described setup) by other off-the-shelf sensors like sensors for light, gas, sound-pressure or magnetic fields.
- The present actuators (e.g. heat lamps) can be replaced by light- or gas-emitters, vibrators, electromagnets and others for use in different types of bioassays.
- It is possible to establish different gradients of different environmental parameters (e.g., temperature AND light) within one setup to investigate effects of combined environmental influences on the behaviour of animals; this is especially interesting for behavioural changes or behavioural disorders based on several unknown parameters (e.g. colony collapse disorder).
- The effect of the given environmental conditions can be
investigated by observing easy-to-measure (behavioural) parameters like moving
speed, orientation, average or relative position of the animals over time, the
area covered by groups of animals or the probability of animal-to-animal
interactions within specific zones and during different experimental phases;
these measurements can be evaluated both manually or automatically.
The given setup allows experiments under well-defined and controlled laboratory experimental conditions. The extent to which the method is adaptable and usable for outdoor experiments is yet to be investigated.
A shortcoming of the current setup is the fact that the heat bulbs have to be positioned at the arena wall lest they obscure parts of the floor, as the camera is mounted on top of the arena. This implementation confines the heat spots to the wall area. If a heat spot needs to be established at a central position, alternative filming methods must be considered. For instance, the camera could be mounted at a flatter angle or two cameras could be used to create a confluent image of the arena floor. Both methods entail additional post-processing of video data (i.e. correction of image distortion or blending of partial images). This is, however, a minor effort to overcome this current limitation when more freedom in the positioning of the heat spots is required. Another shortcoming is the necessity to have basic knowledge in electronics (e.g. reading a datasheet) and soldering techniques (e.g. usage of a soldering iron), which can take some time (several days) to learn.
The setup can be easily scaled for use with different species (e.g. ants, wasps, bumble bees or even mammals) by simply re-adjusting the size of the arena and the density of the temperature sensors. If the sensors are integrated into pre-structured honey bee hives it is even possible to perform the experiments inside a colony. The use of the arena is not restricted to the investigation of thermal gradients. In fact, the quality of the gradient can easily be adapted by replacing the heat-bulbs by other types of actuators, e.g. Peltier-elements, wind machines, pheromone evaporators, magnetic field generators, sound emitters, food dispensers and so on. The sensor array can be adapted accordingly to measure the gradient and provide the feedback for its automatic maintenance.
In combination with online image tracking even a reactive experimental setup is possible. In this setup, the experimenter can pre-define a set of rules according to which the temperature gradient changes once a deliberate number of bees have aggregated at a given place. This way, experiments regarding reaction time and adaptation to environmental fluctuations can be performed.