Pollen Traps

Besides production, a pollen trap is also used as a measuring and monitoring tool: the amount, colour and composition of pollen collected at short, regular intervals show which plants the bees are working, how strong the source is and what pesticide risk exists around the apiary. This page explains how to choose a trap for monitoring, how to standardise sampling and how to interpret the results.

What does a pollen trap do as a monitoring tool?

The hive entrance is a mirror of the vegetation around the apiary. The pellets that fall into the trap drawer are a concrete sample of where the foragers flew that day. For production a trap runs for days; for monitoring, short and regular sampling windows are enough. In this way comparable data are collected all year while the colony's protein intake is barely affected.

• Tracking the pollen flow: Shows in which weeks pollen is plentiful and in which it is scarce; lets you draw up your own apiary's pollen calendar.
• Identifying the plant source: Pellet colour gives a rough clue; microscopic examination gives definite information.
• Comparing apiary sites: The amount and diversity of pollen collected by colonies at different sites in the same period can be compared.
• Monitoring residues: Pollen samples are among the best materials for laboratory testing of the agricultural pesticides the bees are exposed to.

Which pollen trap should you choose for monitoring?

The main aim in measurement is comparability. So it matters less that the trap is highly efficient than that it works the same way every time.

• Same model: Use the same type of trap with the same hole size on all the hives to be compared. Different models strip off pollen at different rates.
• Drawer that empties completely: A flat-bottomed drawer that is easy to pull out and leaves no pollen in its corners ensures the sample is taken in full.
• Mesh cover: Fine mesh above the drawer stops bees reaching the fallen pollen and taking it back; without the mesh the measurement comes out short.
• On–off mechanism: A trap that can be disabled while the grid stays on the hive can be left in place between sampling days without disturbing the colony.
• Protection from rain and sun: A sample that gets wet or sits in the sun deteriorates, and its weighing and analysis become unreliable.

How do you take pollen samples step by step?

1. Choose colonies: Choose several healthy colonies of similar strength, ideally with queens of the same age. Data from a single colony can be misleading.
2. Fix the schedule: For example, run the trap one day a week, from morning to evening or for exactly 24 hours. Use the same duration for every measurement.
3. Collect and weigh: Empty the drawer at the end of the window and record the weight of the fresh pollen. Weighing should be done the same day, on the same scale.
4. Take a subsample: The pollen is mixed thoroughly and a subsample of a set weight is taken; this is sorted by colour and the share of each colour group is weighed.
5. Keep records: Note the date, time window, weather (temperature, wind, rain), colony number and the flowering observed.
6. Freeze the analysis sample: The part going to the laboratory is put in a clean, labelled container, frozen immediately and delivered without breaking the cold chain.
7. Close the trap: When sampling is finished the trap is disabled; the colony goes on carrying in its pollen normally.

How do you interpret pollen measurement results?

A trap strips off not all the incoming pollen but a variable part of it. This proportion varies with the trap model, bee race, pellet size and the state of the colony. So the measurements do not reflect the colony's total pollen intake, but they do meaningfully reflect comparisons made with the same set-up.

How do you take a pollen sample for residue monitoring?

Bees can carry pollen from treated plants within their flight range. If colony losses or mass bee deaths in front of the hives are seen during spraying periods, a fresh pollen sample is valuable evidence for investigating exposure.

• Use a food-grade container that can be labelled and has never been in contact with chemicals.
• Keep the sample from each colony and each date separate; do not mix samples.
• Freeze the sample immediately; a sample left at room temperature deteriorates and gives analysis errors.
• If necessary, also take samples of dead bees and comb in separate containers; in cases of mass deaths, report to the official veterinary service / local agriculture authority.

Does monitoring weaken the colony?

Sampling in short windows does not noticeably affect the colony, because the trap runs for only a few hours or a day. Even so, sampling frequency should be reduced for weak and newly split colonies and in periods critical for pollen, such as early spring and late summer. Leaving the trap permanently open for monitoring is unnecessary and reduces brood rearing.

Common mistakes

• Comparing different trap models: You cannot tell whether a difference comes from the trap or the environment.
• Changing the sampling time: Data from 6 hours one day and 24 hours another cannot be compared.
• Treating colour as definite species information: Colour is only a clue.
• Letting the analysis sample sit: Residue and microbiology results lose their meaning.
• Not recording the weather: The low value of a rainy day may be mistaken for a dearth.