The writing on the pollen

By Athayde Tonhasca

Palynology, from the Greek palynō (‘sprinkle’), is the study of microscopic organic particles such as spores, planktonic organisms and pollen. The branch of palynology focussed on pollen contained in honey is called melissopalynology – the ‘melisso’ part refers to bees, from the Greek mélissa for ‘bee’. This tongue-twister sounds as arid and academic as a study subject could be, but this is not the case. By examining the pollen in a sample of honey, it is possible to determine its purity, geographical location and floral sources. Melissopalynology is a tool to combat fraud and inaccurate labelling of honey, which is handy if you want to buy pure Elvish honey from Turkey, Manuka honey from New Zealand, or other expensive honey bee products. 

Morphology of different pollen from honey samples © Obigba, S.O. 2021. IntechOpen 10.5772/intechopen.97755

Melissopalynology has other applications. It can be used to assess climatic conditions such as rainfall and temperature at the honey’s place of origin, or tell us about environmental changes. This is particularly useful in light of the rapid losses of natural habitats around the world, mostly because of agricultural expansion and intensification.

Half of the world’s habitable land is used for agriculture © OurWorldinData.org

By comparing pollen in honey samples from 1952 and 2017, researchers recorded a profound shift in the most important flower sources for honey bees in the UK. White clover (Trifolium repens) was present in 74% of the 1954 honey samples, but it decreased to about 30% in 2017. Brambles (Rubus fruticosus agg.) and related species were found in 5% of the 1954 samples, but in 2017 they became the most foraged plants.

Predominant and secondary honey bee pollen sources in 1952 (left) and 2017 © Jones, L. et al. 2021. Communications Biology 4, 37

These changes in honey bee preferences have reasons: with the intensification of managed grasslands, crop rotation decreased, and the use of fertilizers and herbicides increased. So clovers became less abundant; countryside surveys revealed a 13% decrease of white clover distribution from 1978 to 2007. Changes in the rural landscape favoured opportunists like brambles and invasive species such as Himalayan balsam (Impatiens glandulifera) (a great source of nectar), which increased their distributions from 1978 to 2007 by 21 and 100%, respectively.

A change of main course for honey bees; from white clover (L) to brambles © Harry Rose (L) and H. Zell, Wikipedia Creative Commons

A shift in sources of food may not sound too bad; honey bees still have their flowers. But not all flowers are equal: brambles have lower levels of proteins and essential amino acids than white clover. Honey bees may compensate for this nutritional deficit, but that requires more time and energy spent on foraging.

Pollen is the main source of proteins, fat, minerals and vitamins for honey bees and many other pollinators. But it is also a rich source of information: pollen attached to museum specimens has helped us understand changes in the distribution and abundance of bumble bees and other pollinators. Taxonomists, earth scientists, climatologists, archaeologists, palaeontologists, and criminal investigators – those examining suspect honey, or those tracing a body, dead or alive, to specific surroundings – have also tapped into the data extracted from pollen. So, a shout out to palynologists, who understand so well the value of those grains of plant dust.

Palynologist Dr Kat Holt doing climate research © Phys.org