18.104.22.168. Analysing pollen trap contents
Pollen pellets from many plant species can be identified by colour (Fig. 9). To establish the colour of the pellets of interest it is best to catch bees with pollen pellets from the crops of interest and remove their pellets so they can then be used as standards for comparing with pellets in the tray of the pollen trap. It is important to note that the colour of pellets may change depending on the light by which they are viewed and when they dry (Kirk, 2006). Because the colours of pellets from some plant species are sometimes similar, it is often necessary to measure the size of the pollen grains making up the pollen pellet and study the pollen grains’ surface features microscopically to establish whether the trap contents can be sorted by eye (see section 3.1.1.).
Because of the large amounts of pollen that may be
trapped at times, it may be necessary to subsample the pollen trap contents.
The contents of a trap are often layered as bees collect pollen from different
plant species at different times of day. It is therefore necessary to mix the
contents of the trap thoroughly before subsampling. If determining the weight
of different pollens trapped rather than the number of pellets trapped, it is
necessary to first dry samples to a constant weight as their moisture content
may vary between species, time of day, and between days. Samples of pollen
pellets can be stored for short periods of time at room temperature. However
they may eventually develop mould making them difficult to analyse. It is
therefore good practice to freeze samples if they are not going to be analysed
at the time of collection.
Fig. 9. Pollen pellets