4.2.1. Marking bees in the crop
This can be achieved by catching bees on the crop, marking them, and opening hives in the evening and searching for marked bees. Bees will usually need to be immobilized before marking. This can be done by chilling the foragers, anoxiating them with CO2 or anesthetizing them with chloroform. Care needs to be taken when choosing to use CO2 as it has been reported to inhibit pollen collection (Ribbands, 1950, Brito et al., 2010).
Acrylic paints can be used to mark bees if they only need to be marked for a single day as the paint may wear off after this time. Acetone based paints will last longer. By using a range of colours and positions of spots on the thorax and abdomen it is possible to individually and distinctively mark large numbers of bees. An alternative, more costly method, is to use purpose-made plastic queen tags glued on the thorax of worker honey bees (Fig. 12). As there are often a large number of bee colonies foraging from a crop, it is usually necessary to mark large numbers of bees to obtain adequate recovery rates.
Color-coded ferrous tags glued to the thoracic dorsum
of an individual forager in the field can be retrieved at the hive entrance
with magnets (Gary,
1971). This technique enables studies of spatial distribution of bees in an
Fig. 12. Foragers with queen tags