Pollen, the fine, powdery substance produced by flowering plants, represents the male reproductive cells of flowers. For bees, pollen serves as a fundamental substance, playing a central role in their survival and the functioning of their colonies. Its importance extends beyond the individual bee, underpinning broader ecological processes essential for many plant species.
Pollen for Bee Nutrition
Pollen is the primary source of protein, fats, vitamins, and minerals for bees, making it a complete food source for the colony. Its composition varies, with 20-25% crude protein considered beneficial for bee health. This rich nutritional profile is crucial for the development of young bees, specifically the larvae. Immature bees are fed “bee bread,” which is the main source of protein for their growth.
Adult bees also rely on pollen for various physiological functions. Newly emerged bees consume bee bread to complete their physical development, and a diet of high-protein pollen enhances the longevity of worker bees. Nurse bees consume significant amounts of pollen to develop their hypopharyngeal glands, which produce royal jelly. This protein-rich secretion is fed to all larvae for their initial days and exclusively to the queen bee throughout her larval stage, supporting her growth and reproductive capacity.
Pollen brought to the hive is mixed with nectar and bee salivary secretions, then packed into honeycomb cells where it undergoes a lactic fermentation process. This fermented product, known as “bee bread,” is more digestible for the bees due to the breakdown of the pollen grain’s tough outer layers. Bee bread serves as a preserved, long-term food supply, allowing the colony to sustain itself during periods when fresh pollen is scarce.
Pollen Collection and Storage
Worker bees have specialized structures to efficiently gather and transport pollen. On their hind legs, honey bees possess “pollen baskets” (corbiculae), which are concave areas surrounded by stiff hairs. As a bee visits flowers, pollen adheres to its body, aided by a slight electrostatic charge. The bee then brushes the pollen, moistens it with nectar or honey, and packs it into these pollen baskets.
The process of loading the corbiculae involves coordinated movements of all six legs. Pollen is transferred from the forelegs to the middle legs, and then combed and pressed onto the corbiculae of the hind legs. Once the pollen baskets are full, the bee returns to the hive. Upon arrival, the foraging bee deposits these pollen pellets into empty honeycomb cells, often located at the interface between the brood and stored honey.
Inside the hive, worker bees process the collected pollen. They pack the pellets firmly into the cells, often using their heads, and cover them with a thin layer of honey and wax. This packing and sealing process, along with enzymes and microorganisms, initiates the fermentation that transforms pollen into bee bread. This stored bee bread provides a vital reserve, ensuring continuous nutrition for the hive, especially during times of low floral availability.
Pollen’s Role in Plant Reproduction
While bees use pollen for sustenance, their activity plays a significant role in plant reproduction, illustrating a mutualistic relationship between bees and flowering plants. As bees forage, pollen grains from a flower’s anthers adhere to their bodies. When the bee moves to another flower, some of these pollen grains rub off onto the stigma.
This transfer of pollen from the anther to the stigma is known as pollination, a fundamental step for fertilization and the production of seeds and fruits in many flowering plants. Bees are highly effective pollinators because they exhibit “flower constancy,” meaning they tend to visit flowers of the same species during a single foraging trip. This behavior increases the likelihood that pollen is transferred between compatible plants, maximizing reproductive success for the plant species.
The co-evolution of bees and flowers has resulted in plants developing various features, such as colors, scents, and shapes, to attract bees. In return for the nectar and pollen rewards, bees facilitate plant reproduction, contributing to genetic diversity. This process supports food webs and biodiversity, as many fruits, vegetables, and seeds depend on bee pollination. Without bees, many plant species would struggle to reproduce, leading to ecological and agricultural consequences.