5.4. Direct surface measurements of target
1. Photographic records of bees on combs will vary according to time of day and bee foraging activity. For this reason, it is important to control for this effect, either by limiting observations to a narrow time window on successive days, randomly assigning time of inspection such that day effect is equitably and randomly distributed across treatments, or closing hive entrances in the early morning until bees are counted. This constraint does not apply to cell-based resources such as brood, honey, or pollen.
2. Hives are lightly smoked, opened, and frames permanently labelled: frame 1 side A or B, frame 2 side A or B, and so forth.
3. Each frame is removed and photographed on each side in such a way that colony and frame labelling are recorded. It is preferable to use a custom-built holding mount where each comb is placed in a holder and the distance between the comb and camera fixed.
4. Combs are first photographed with bees. If additional comb resources are of interest, then the bees are brushed into a holding box and the comb photographed again to expose brood, honey, or pollen. It is important to avoid brushing bees back into the hive because this will affect the photographic bee record of subsequent frames. Eggs and 1 – 3 day old larvae may be hard to see and if these brood stages are the objective of the study it is preferable to apply digital cell / location recognition software.
5. The digital photos are analysed using a computer program such as ImageJ, available free at . Post-hoc, the photos are uploaded in the computer and analysed as diagrammed in Fig. 11.
6. The results of the calculated area is in dm2
or cm2 depending on the scale that has been set. To finish the
analysis, the number or bees or cells are derived with Excel or a similar
spreadsheet program using the expected density of bees per cm2 or
cells per cm2 given in Table 2. Surface data from this digital
analysis could be inserted into Column G in Fig. 6 - 8.
Fig. 11. Outline of the method of Cornelissen et al. (2009). Flow chart of computer assisted image analysis applying ImageJ software. Step 2 can be skipped by making the photos in a fixed position at which the distance between camera and frame is constant.