Abstract
The least understood aspects of the nutritional needs of bees are the elemental composition of pollen and the bees’ need for a stoichiometrically balanced diet containing the required proportions of nutrients. Reduced plant diversity has been proposed as an indirect factor responsible for the pollinator crisis. We suggest stoichiometric mismatch resulting from a nutritionally unbalanced diet as a potential direct factor. The concentrations and stoichiometric ratios of C, N, S, P, K, Na, Ca, Mg, Fe, Zn, Mn, and Cu were studied in the bodies of honeybees of various castes and sexes and in the nectar and pollen of various plant species. A literature review of the elemental composition of pollen was performed. We identified possible co-limitations of bee growth and development resulting mainly from the scarcity of Na, S, Cu, P and K, and possibly Zn and N, in pollen. Particular castes and sexes face specific limitations. Concentrations of potentially limiting elements in pollen revealed high taxonomic diversity. High floral diversity may be necessary to maintain populations of pollen eaters. Single-species crop plantations, even if these species are rich in nectar and pollen, might limit bee growth and development, not allowing for gathering nutrients in adequate proportions. However, particular plant species may play greater roles than others in balancing honeybee diets. Therefore, we suggest specific plant species that may (1) ensure optimal growth and production of individuals by producing pollen that is exceptionally well balanced stoichiometrically (e.g., clover) or (2) prevent growth and development of honeybees by producing pollen that is extremely unbalanced for bees (e.g., sunflower). Since pollen is generally poor in Na, this element must be supplemented using “dirty water”. Nectar cannot supplement the diet with limiting elements. Stoichiometric mismatch should be considered in intervention strategies aimed at improving the nutritional base for bees.
Highlights
The growth and development of any organism may be limited by unbalanced stoichiometry, namely unbalanced proportions of atoms of chemical elements in food that reflect proportions of physiologically important organic molecules [1,2,3,4]
Considering the possible sources of chemical elements gathered by bees, it can be assumed that the stoichiometry of pollen is the key factor influencing the nutritional balance of larval food, since (1) energy is readily available from nectar; (2) pollen is almost the exclusive source of non-carbon elements for bees; (3) elements are conserved, i.e., they cannot be converted into other elements; and (4) organic compounds are processed and recycled by jelly-producing nurse bees
The study consisted of two separate research tasks, (1) a field experiment investigating the possible limiting effects imposed on bee development by the stoichiometry of available and Ecological stoichiometry of pollen for honeybees collected pollen and (2) a literature review investigating the variance in the stoichiometrically limiting effects of the pollen produced by different plant taxa
Summary
The growth and development of any organism may be limited by unbalanced stoichiometry, namely unbalanced proportions of atoms of chemical elements in food that reflect proportions of physiologically important organic molecules [1,2,3,4]. Maintaining the balance between matter supply and demand is crucial for the development of an organism and, building the body of its adult form In this context, herbivores must cope with stoichiometric mismatches resulting from the fundamental differences between the elements ratios of their tissues and food [1,2,7] (see [5,8,9] for comparison with other feeding guilds). Considering the possible sources of chemical elements gathered by bees (nectar, pollen, water), it can be assumed that the stoichiometry of pollen is the key factor influencing the nutritional balance of larval food, since (1) energy is readily available from nectar; (2) pollen is almost the exclusive source of non-carbon elements for bees; (3) elements are conserved, i.e., they cannot be converted into other elements; and (4) organic compounds are processed and recycled by jelly-producing nurse bees. For organisms that feed on plant matter, the quality (elemental ratios) may be more limiting than the quantity of the plant matter [2,9,17]; in other words, the growth and development of these organisms may not be limited primarily by energy but instead by the proportion of the body-building nutrients in food
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