6.2.3. Standard two-way shuttle box construction
An example of a honey bee shuttle box is shown in Fig. 6. The apparatus is made from plastic. Infra-red photocell-detector circuits automatically monitor shuttle responses. The photocells must be in the infra-red range, so not to attract the bee. The aversive stimulus is typically electric shock but odours also are used. An olfactory shuttle box for insects is described by Abramson et al. (1982) and modified for honey bees (Abramson, 1986). The honey bee can be placed in the shuttle box in several ways. The easiest is to capture bees (see section 2.1.) and narcotize them (section 2.2.). When the bee is less active it can be safely placed in the apparatus. Alternatively, an active bee placed inside of a container or vial can be lured into the shuttle box by light. Light can also be used to induce the bees to leave the apparatus when the experimental session is completed. Luring the bee to the shuttle box eliminates the need to narcotize it.
When constructing and using a shuttle box there are some important issues you must consider. For example, great care must be given to the dimensions of the apparatus, how stimulus cues are presented if punishment and signalled avoidance paradigms are used, and the placement of photocell-detector pairs. A disadvantage of the shuttle box is that it represents an unnatural situation for the honey bee and the bee is often highly active when placed inside the shuttle box.
For technical details, the reader is advised to look at the Abramson (1986) and Agarwal et al., (2011) papers before constructing their own shuttle box. If shock is used rather than odours, it is critical that the bee stays in contact with the shocking surface. If the ceiling of the apparatus is too high, the bee will quickly learn to walk on the ceiling and/or keep a few legs on the shocking surface and the rest on the walls of the apparatus. In both situations the bee is not receiving the programmed intensity and duration of shock. This situation is easily eliminated by having a ceiling just a few millimetres above the bee.
Another issue related to apparatus size is that there must be enough room for the bee to turn around and re-enter the compartment it just came from. The bee will be highly active making many responses and often moving from end to end. If the width of the shuttle box is to narrow, the bee will find it difficult to shuttle between compartments. This is readily seen, because the bee will try and walk backwards. This problem can be eliminated by using a suitable width between the walls.
For the shuttle box to function effectively, the bee must have a cue that it entered a new compartment. The cue can be as simple as small strips of plastic that it steps over, a sloping roof that requires the bee to "duck under" or visual stimuli. One method to present visual stimuli is to set the shuttle box on a flat screen computer monitor. However, this will only work if you are using shock grids. An alternative is to place coloured plastic strips under the grid that are manually changed at the appropriate time (Agarwal et al., 2011).
The final issue to consider when using a shuttle box is the photocells and their placement. A photocell-detector pair should be placed on either side of the mid-line of the apparatus approximately a bee’s length. This length ensures that the experimenter has a clear definition that the bee fully entered a compartment. The photocell circuit should also be carefully designed. It is not a trivial problem to get a bee to trip a photo beam. Consideration must also be given to the background illumination in the area where the shuttle box is to be placed. If the level of infra-red in the background illumination is too high, it might activate the detector without a bee being present.