Pollen is produced by seed plants as part of their sexual reproduction, containing the male gametes necessary for fertilization. This material is collected for a variety of purposes, including the monitoring of airborne allergens, supporting commercial beekeeping, and conducting specialized plant breeding research. The specific method used to gather this biological material is entirely dependent on the intended use, which dictates the required purity, quantity, and scale of the collection.
Manual Collection Techniques
Collecting pollen for controlled plant breeding or small-scale scientific analysis requires precision, focusing on isolating the material from individual plants or flowers. A common technique involves using fine-tipped tools, such as tweezers or forceps, to carefully remove the anthers. The anthers are then allowed to dry until they naturally release the pollen grains onto a collection surface, like a glass slide or a small vial.
Alternatively, a soft, fine brush can be used to gently sweep the pollen directly from the anther onto the desired surface. Tapping the flower over parchment paper or a container is another simple method that causes mature pollen to fall due to gravity. For laboratory settings, specialized miniature vacuum devices are sometimes employed to delicately suction pollen directly from the flower, maximizing the yield. All tools must be sterilized between samples to prevent the cross-contamination of genetic material.
Collection Using Hive Traps
For large-scale collection, primarily for commercial beekeeping to harvest pollen for consumption, specialized hive traps are used. A pollen trap is a device fitted directly over the entrance of a beehive, requiring returning forager bees to crawl through a screen or a grid of small openings. The screen is engineered with a specific diameter that is just large enough for the bee to pass through without causing injury.
As the bees squeeze through these openings, the edges of the grid gently scrape the pollen pellets, which are packed onto the bees’ hind legs, off their bodies. The dislodged pellets then fall into a ventilated collection tray positioned below the screen. These traps are designed to collect only a portion of the incoming pollen, ensuring the colony still receives sufficient food for its own development and brood rearing. Beekeepers must manage the trap use carefully, installing them only on strong colonies and only for short periods during peak pollen flow, to avoid stressing the bee population.
Atmospheric Pollen Sampling
Monitoring airborne pollen is a distinct collection method, focusing on capturing grains already dispersed in the atmosphere for purposes like allergy forecasting and environmental research. One simple method involves the use of a gravity slide, which is a glass slide coated with an adhesive material exposed outdoors for a set period. Pollen grains settle onto the sticky surface over time, allowing for a qualitative assessment of what is present.
Volumetric samplers, such as the Hirst-type trap, are the standard for quantitative measurement. This device uses an internal vacuum pump to draw air at a controlled flow rate through an inlet. The airborne particles are then impacted onto a rotating drum or slide coated with an adhesive film. The Rotorod sampler spins two lubricant-coated rods for brief, timed intervals to capture particles by impaction. After collection, the sample is stained and examined under a microscope to identify and count the grains, allowing scientists to report the concentration per cubic meter of air.
Preservation and Storage
Once pollen is collected, proper preservation is necessary to maintain its viability and nutritional quality. Freshly collected pollen contains a high moisture content (20% to 30%), which creates an environment where mold and bacteria can rapidly degrade the sample. The most important initial step is to reduce this moisture content, ideally to 4% to 8%, to halt metabolic processes and prevent spoilage.
This drying can be achieved by spreading the pollen in thin layers and air drying it, or by using specialized low-temperature drying equipment below 40°C (104°F) to protect heat-sensitive nutrients. For short-term preservation, the dried pollen can be stored in a refrigerator around 4°C, which slows the rate of decay. Long-term storage typically involves freezing the pollen in airtight containers, sometimes placed within a desiccator containing a humidity-controlling agent like silica gel. The most effective method for preserving viability over many years is freeze-drying, which removes moisture through sublimation and allows for storage at ultra-low cryogenic temperatures. Accurate labeling of the container is a necessary final step, recording the date, specific source plant, and location of collection.