Feeding on improper plant species might be one of the causes of mass bee die-offs. Biologists from the Jagiellonian University and the University of Life Sciences in Lublin have investigated how the nutritional values of different kinds of plants affect the development of honeybees.
From early spring to autumn, pollinators such as bees can help themselves to an abundant buffet of nectar and pollen served by trees, shrubs, and other flowering plants. Nectar gives them the energy required to perform their daily tasks, while pollen is used as one of the food sources for the young, who need it to grow and develop. If a baby bee wants to grow up to become a healthy adult, it needs high quality food. And there’s the problem.
Pollen – a powdery substance comprising pollen grains which produce male sperm cells. It’s gathered by bees in the form of pollen baskets. It’s frequently incorporated into human diet as a source of valuable salutogenic (health-improving) substances. A bee can transport one pollen basket on each of its hind legs – these little balls can weigh up to 10 milligrams and contain millions of grains of pollen from several hundred plants.
Nectar – a secretion of plant glands, composed mostly of water-soluble saccharides. Animals that feed on nectar accidentally dirty themselves with pollen. When they travel around in search for more food, they cause the male sperm cells in pollen to fertilise female reproductive organs in other plants of the same species. This is how pollination takes place.
The majority of solitary bee larvae feed directly on pollen delivered by a mother bee (not to be confused with a queen bee). Honeybees are a different case altogether: their nursing workers feed their young with jelly, a pre-digested mixture of nectar, pollen, and water. Nectar provides the high-energy glucose and fructose, while pollen is a source of building material for the bodies of the larvae. The quality of pollen determines the overall quality of food.
Jelly is made of various organic substances: saccharides, fats, proteins, vitamins, amino acids, and enzymes. All of those chemical compounds are built from elements like carbon, hydrogen, oxygen, nitrogen, phosphorus, sodium, potassium, zinc, and about twenty others.
Saccharides are composed solely of carbon, hydrogen, and oxygen. Other substances feature atoms of other elements, and all of them are needed by bee larvae in order to properly develop their own bodies. This is where pollen comes in: it is the source of those substances. But do all plants produce pollen that is rich in the necessary nutrients? No – and that is the fulcrum of the issue.
Mixing it up
Pollen produced by different species of plants provides bees with varying amounts of certain chemical elements – but the proportions are often inadequate. ‘We based our study on ecological stoichiometry, a method which treats atoms as microscopic building bricks of all organisms’, explained Dr Michał Filipiak from the JU Institute of Environmental Sciences. ‘When an organism grows, it can only use resources that can be found in the environment – and in most cases, there is a simultaneous excess of some elements and shortage of others. Bearing that in mind, we compared the atomic structure of bodies of honeybees with the chemical composition of various types of pollen. It turned out that the bees are particularly in need of seven elements: sodium, sulphur, copper, phosphorus, potassium, nitrogen, and zinc. And, naturally, different plants produce pollen that contain different elements in different amounts’, he continued. ‘So what does it mean? Let’s imagine there’s Plant A and Plant B. Pollen A is rich in sulphur, but lacking in potassium. The converse is true for Pollen B. Collecting pollen from only one plant would negatively impact the larva’s health; however, combining pollen from both plants gives it a balanced meal. Because of this, we should stop thinking about ‘bee-friendliness’ of plants in terms of how much nectar and pollen they produce, but rather how high their quality is’, Dr Filipiak added.
Monoculture may hamper the bees’ development by restricting their dietary options. For instance, sunflower pollen contains very little phosphorus, an element crucial for building ribosomes and RNA, which are responsible for synthesising proteins in cells and aiding in the growth of the entire organism. Honeybees forced to live solely off of sunflower pollen develop more slowly and die more frequently. We should make sure that monoculture plantations are situated in the neighbourhood of high quality pollen plant species, such as clover. ‘Clover is perfect, as its pollen contains a high concentration of all the necessary elements – except sodium, but that’s true for all plants. Bees usually look for sodium in water, particularly in polluted places like puddles. Anyway, clover is not the only plant that’s good for bees. In our study, we enumerated about twenty other species from around the world. One of them, for example, is eucalyptus, but those are quite hard to come by in Poland’, said Dr Filipiak.
The chemistry of pollen
The decrease of plant diversity and disappearance of some species is commonly thought to be one of the causes of the dwindling numbers of pollinators worldwide. The research study conducted by biologists form the Jagiellonian University and University of Life Science sin Lublin seems to corroborate that: indeed, the lack of a balanced diet leads to underdevelopment and eventual death of honeybees. Currently, governments try combat this phenomenon by curbing the use of pesticides and improving the quality of food sources. Knowing which elements are crucial for bees’ diet is something that can put into practice in the efforts to help the industrious insects.
A few statistics
It’s estimated that about 80% of wild plants and 75% of cultivated plants are directly dependent on pollinators. Without them, they won’t be able to produce seeds and fruit. The worth of labour performed by bees worldwide is estimated at 153 million euro per year. This is equal to 9.5% of the worth of the entire agricultural produce for all people on Earth in 2005.
‘This is why we constantly strive to gain a better understanding of the complex relations between the quality of pollen and number and diversity of pollinators. Presently, we’re studying solitary bees by feeding them mixed pollen with varying amounts of different chemical elements. In this way, we can see what happens when they lack certain elements. We’ll have the results in about two to three years. Implementing our solutions will offer better protection to pollinators, and in consequence secure the future of our food. It wouldn’t be wise to ignore the dietary requirements bees, and failing to understand their biology can really blow up in our faces’, summarised Dr Filipiak.
Photograph at the top: honeybees at the entrance to their hive. One of them is carrying a pollen basket that will be safely stored inside. Photograph by Paweł Dudzik.
The article is based on the results of the project Ecological stoichiometry of the honeybee: pollen diversity and adequate composition are needed to mitigate limitations imposed on the growth and development of bees by pollen quality, published in the PLOS ONE journal.
Original text: www.nauka.uj.edu.pl